[wasm][debugger] Support optional parameters in external methods

[ilonatommy]

Sample external function with optional parameter:
public string[] Split (char separator, int count, StringSplitOptions options = System.StringSplitOptions.None);

Reproduction:

var strToSplit = "ab-cd";

How to test in debugger watch:
strToSplit.Split('-', 1);
strToSplit.Split('-', 1, System.StringSplitOptions.None);
Test in OnCallFrameTests:
EvaluateMethodWithLinq

How to fix:
GetMethodInfo should return not-null value for external methods. Either fix loading symbols

runtime/src/mono/wasm/debugger/BrowserDebugProxy/MonoProxy.cs

Line 1081 in 4fd5132

if (urlSymbolServerList.Count == 0)

or fix saving and extracting method:

runtime/src/mono/wasm/debugger/BrowserDebugProxy/MonoSDBHelper.cs

Line 781 in 4fd5132

var method = asm.GetMethodByToken(methodToken);

.

Make sure that Linq functions work both in headless mode in tests and manually in browser.

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Issue Details

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Sample external function with optional parameter:
public string[] Split (char separator, int count, StringSplitOptions options = System.StringSplitOptions.None);

Reproduction:

var strToSplit = "ab-cd";

How to test in debugger watch:
strToSplit.Split('-', 1);
strToSplit.Split('-', 1, System.StringSplitOptions.None);

How to fix:
GetMethodInfo should return not-null value for external methods.

Author:	ilonatommy
Assignees:	-
Labels:	arch-wasm, area-Debugger-mono
Milestone:	-