[linker] improve method detection in FixAbstractMethodsStep

[radekdoulik]

The forms team run into an issue with debugger in VS [1]. During
investigation it turned out that our FixAbstractMethodsStep injects 2
methods, which were not needed, as the methods were already
implemented. The bug itself looks like an issue, where original mdb
file was used in the apk, instead of the one written by our linker.

This change improves the method detection, where method name starts
with global::. In this particular case it were these methods:

global::Android.Views.View.IOnTouchListener.OnTouch
global::Android.Views.View.IOnClickListener.OnClick

[1] https://bugzilla.xamarin.com/show_bug.cgi?id=59293

[jonpryor]

As discussed elsewhere, I do not like explicit string comparison, as it's likely to be wrong. For example, the IL name of explicitly-implemented interface methods is compiler-specific, so even if global::Android.Views.View.IOnTouchListener.OnTouch works now, it very likely will not work with e.g. a VB.NET-generated assembly or F#-generated assembly.

Instead, the fix should probably involve MethodDefinition.Overrides, and check to see if the MethodDefinition overrides the interface's MethodDefinition.

[dellis1972]

build

[radekdoulik]

I will also extend the test case. I need to fix a linker bug first though.

[radekdoulik]

build

[radekdoulik]

added unit test

[jonpryor]

This is compiler-specific, and will fail if/when the compiler changes.

For example, given:

class T : IEnumerable {
	IEnumerator global::System.Collections.IEnumerable.GetEnumerator()
	{
		return null;
	}
}

When compiling the above with mcs, we get:

.method private hidebysig newslot virtual final 
          instance class [mscorlib]System.Collections.IEnumerator 
          System.Collections.IEnumerable.GetEnumerator() cil managed

compare to csc (Roslyn):

  .method private hidebysig newslot virtual final 
          instance class [mscorlib]System.Collections.IEnumerator 
          'global::System.Collections.IEnumerable.GetEnumerator'() cil managed

Use mcs, and this test will break. That's not a good test.

[radekdoulik]

build