[dotnet] Avoid using install_name_tool on macOS and specify correct rpath instead

[filipnavara]

No description provided.

[chamons]

I'll let @rolfbjarne be primary reviewer on this.

@filipnavara - What prompted this work - There isn't an explanation in the PR itself.

[filipnavara]

Ah, sorry. I forgot to put it in the description. It contributes to fixing issue #9800 and uses a better approach than #9804 to fix the same underlying problem. The comment in the source code around _UpdateDynamicLibraryId explains that it's a temporary hack for a build issue in dotnet/runtime. On macOS the hack is not necessary since the binaries are produced with proper identity (eg. @rpath/libXXX.dylib) in the runtime pack. It works as long as the linking step specifies correct relative paths (the bundle structure is different between iOS and macOS) which this PR fixes.

[rolfbjarne]

build

[rolfbjarne]

build

[monojenkins]

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