Context: dotnet/android#4631
Context: https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=3685184&view=logs&j=b1314ebb-4483-559c-0367-730fc62c4440&t=5022c07e-db44-5ce4-1a38-092215b61c50
Context: 70fc4c0

Commit 70fc4c0 broke use of `jnimarshalmethod-gen.exe` within
xamarin-android and `Mono.Android.dll`, as it allows methods taking
more than 14 parameters to be bound, which results in
`jnimarshalmethod-gen.exe` trying to use an `Action<…>` or
`Func<…>` that takes more than 16 parameters, which isn't allowed:

	EXEC : error : jnimarshalmethod-gen: Unable to process assembly '…/xamarin-android/bin/Release/lib/xamarin.android/xbuild-frameworks/MonoAndroid/v10.0/Mono.Android.dll'
	  An incorrect number of type arguments were specified for the declaration of an Action type.
	  Parameter name: typeArgs
	  System.ArgumentException: An incorrect number of type arguments were specified for the declaration of an Action type.
	  Parameter name: typeArgs
	    at System.Linq.Expressions.Expression.GetActionType (System.Type[] typeArgs)
	    at Java.Interop.MarshalMemberBuilder.CreateMarshalToManagedExpression (System.Reflection.MethodInfo method, Java.Interop.JavaCallableAttribute callable, System.Type type)
	    at Java.Interop.MarshalMemberBuilder.CreateMarshalToManagedExpression (System.Reflection.MethodInfo method)
	    at Xamarin.Android.Tools.JniMarshalMethodGenerator.App.CreateMarshalMethodAssembly (System.String path)
	    at Xamarin.Android.Tools.JniMarshalMethodGenerator.App.ProcessAssemblies (System.Collections.Generic.List`1[T] assemblies)

Update `jnimarshalmethod-gen.exe` so that it *skips* methods which
take more than 14 parameters.  This is to unblock xamarin-android
integrations.

(Hopefully this in itself will be enough for xamarin-android to build.)

Next, *begin* plumbing support for this scenario.

To remove the workaround and get things fully working (failing),
rebuild `jnimarshalmethod-gen.exe` with:

	msbuild /restore tools/jnimarshalmethod-gen/Xamarin.Android.Tools.JniMarshalMethodGenerator.csproj /p:_AllTheArguments=True

Also update `jnimarshalmethod-gen.exe` so that it *optionally* uses
`Mono.Linq.Expressions`, for additional debugging output:

	msbuild /restore tools/jnimarshalmethod-gen/Xamarin.Android.Tools.JniMarshalMethodGenerator.csproj /p:_DumpRegisterNativeMembers=True

(Use `/p:_AllTheArguments=True /p:_DumpRegisterNativeMembers=True`
for both!)

Add a method to `ExportTest.cs` / `ExportType.java` which takes more
than 14 parameters, and update `MarshalMemberBuilder` so that it can
generate the appropriate JNI Marshal Method for such a method.
(This should help avoid the need for xamarin-android integrations to
see what's broken.)

The complexity of supporting more than 14 parameters doesn't like in
`MarshalMemberBuilder`, per-se; `Java.Interop.Export-Tests.dll` runs
just fine when just using `Expression.Lambda(body, bodyParams)`.
Things get much more complicated when `jnimarshalmethod-gen.exe`
enters the picture, and interacts with `MarshalMemberBuilder`.
`jnimarshalmethod-gen.exe` *requires* an "appropriate" delegate type.

Update `MarshalMemberBuilder` to "know about" the `_JniMarshal*`
delegates added in cbb50af, and attempt to use them from the assembly
that is being processed, if they exist.

This got further, resulting in an error that
`_JniMarshal_PPZBCSIJFDLLLLLDFJ_Z` can't be used as a constant (?!).

Address *that* error by updating `App.cs` so that it emits a
`Type.GetType("_JniMarshal_PPZBCSIJFDLLLLLDFJ_Z", true)`.  This allows
`jnimarshalmethod-gen.exe` to execute successfully.

Then we try *running* it, and it fails:

	$ make run-test-jnimarshal
	…
	EXEC : 1) error : Java.InteropTests.MarshalMemberBuilderTest.AddExportMethods […/Java.Interop/build-tools/scripts/RunNUnitTests.targets]
	  Java.Interop.JavaException : com.xamarin.interop.export.ExportType.staticAction()V
	    at Java.Interop.JniEnvironment+StaticMethods.CallStaticVoidMethod (Java.Interop.JniObjectReference type, Java.Interop.JniMethodInfo method)
	    at Java.InteropTests.MarshalMemberBuilderTest.AddExportMethods ()
	    at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
	    at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
	    --- End of managed Java.Interop.JavaException stack trace ---
	  java.lang.UnsatisfiedLinkError: com.xamarin.interop.export.ExportType.staticAction()V
	  	at com.xamarin.interop.export.ExportType.staticAction(Native Method)
	  	at com.xamarin.interop.export.ExportType.testStaticMethods(ExportType.java:26)>

Add more printfs, and we get the problem:

	System.InvalidProgramException: Invalid IL code in Java.InteropTests.ExportTest/__<$>_jni_marshal_methods:__RegisterNativeMembers (Java.Interop.JniNativeMethodRegistrationArguments): IL_0176: ldloc.0

At this point things don't make sense to me.
The `__RegisterNativeMembers()` method is:

	## Dumping contents of `Java.InteropTests.ExportTest::__RegisterNativeMembers`:
	void (JniNativeMethodRegistrationArguments args)
	{
	    Type targetType;

	    targetType = Type.GetType("Java.InteropTests.ExportTest");
	    args.AddRegistrations(new JniNativeMethodRegistration[] {
	        new JniNativeMethodRegistration("funcIJavaObject", "()Ljava/lang/Object;",
	            Delegate.CreateDelegate(System.Func`3[System.IntPtr,System.IntPtr,System.IntPtr], targetType, "FuncIJavaObject")),
	        new JniNativeMethodRegistration("funcInt64", "()J",
	            Delegate.CreateDelegate(System.Func`3[System.IntPtr,System.IntPtr,System.Int64], targetType, "FuncInt64")),
	        new JniNativeMethodRegistration("action", "()V",
	            Delegate.CreateDelegate(System.Action`2[System.IntPtr,System.IntPtr], targetType, "InstanceAction")),
	        new JniNativeMethodRegistration("actionIJavaObject", "(Ljava/lang/Object;)V",
	            Delegate.CreateDelegate(System.Action`3[System.IntPtr,System.IntPtr,System.IntPtr], targetType, "InstanceActionIJavaObject")),
	        new JniNativeMethodRegistration("staticAction", "()V",
	            Delegate.CreateDelegate(System.Action`2[System.IntPtr,System.IntPtr], targetType, "StaticAction")),
	        new JniNativeMethodRegistration("staticActionFloat", "(F)V",
	            Delegate.CreateDelegate(System.Action`3[System.IntPtr,System.IntPtr,System.Single], targetType, "StaticActionFloat")),
	        new JniNativeMethodRegistration("staticActionIJavaObject", "(Ljava/lang/Object;)V",
	            Delegate.CreateDelegate(System.Action`3[System.IntPtr,System.IntPtr,System.IntPtr], targetType, "StaticActionIJavaObject")),
	        new JniNativeMethodRegistration("staticActionInt", "(I)V",
	            Delegate.CreateDelegate(System.Action`3[System.IntPtr,System.IntPtr,System.Int32], targetType, "StaticActionInt")),
	        new JniNativeMethodRegistration("staticActionInt32String", "(ILjava/lang/String;)V",
	            Delegate.CreateDelegate(System.Action`4[System.IntPtr,System.IntPtr,System.Int32,System.IntPtr], targetType, "StaticActionInt32String")),
	        new JniNativeMethodRegistration("staticFuncMyLegacyColorMyColor_MyColor", "(II)I",
	            Delegate.CreateDelegate(System.Func`5[System.IntPtr,System.IntPtr,System.Int32,System.Int32,System.Int32], targetType, "StaticFuncMyLegacyColorMyColor_MyColor")),
	        new JniNativeMethodRegistration("staticFuncThisMethodTakesLotsOfParameters", "(ZBCSIJFDLjava/lang/Object;Ljava/lang/String;Ljava/util/ArrayList;Ljava/lang/String;Ljava/lang/Object;DFJ)Z",
	            Delegate.CreateDelegate((Type)Type.GetType("_JniMarshal_PPZBCSIJFDLLLLLDFJ_Z", true), targetType, "StaticFuncThisMethodTakesLotsOfParameters"))
	    });
	}

The offending IL fragment:

	…
	IL_0161:  ldstr      "staticFuncThisMethodTakesLotsOfParameters"
	IL_0166:  ldstr      "(ZBCSIJFDLjava/lang/Object;Ljava/lang/String;Ljava/util/ArrayList;Ljava/lang/String;Ljava/lang/Object;DFJ)Z"
	IL_016b:  ldstr      "_JniMarshal_PPZBCSIJFDLLLLLDFJ_Z"
	IL_0170:  ldc.i4.1
	IL_0171:  call       [mscorlib]System.Type [mscorlib]System.Type::GetType(string, bool)
	IL_0176:  ldloc.0
	IL_0177:  ldstr      "StaticFuncThisMethodTakesLotsOfParameters"
	IL_017c:  call       [mscorlib]System.Delegate [mscorlib]System.Delegate::CreateDelegate([mscorlib]System.Type, [mscorlib]System.Type, string)
	IL_0181:  newobj     instance void [Java.Interop]Java.Interop.JniNativeMethodRegistration::.ctor(string, string, [mscorlib]System.Delegate)

I don't understand where the `ldloc.0` is coming from, or why it's
there.

Punting a complete fix for now.

To repro the crash:

	$ rm -Rf bin/TestDebug
	$ msbuild
	$ msbuild /restore tools/jnimarshalmethod-gen/Xamarin.Android.Tools.JniMarshalMethodGenerator.csproj /p:_AllTheArguments=True /p:_DumpRegisterNativeMembers=True
	$ make run-test-jnimarshal