[tests] rework JavaObjectTest, use FinalizerHelper from mono/mono

[jonathanpeppers]

Context: dotnet/runtime#60638 (comment)
Context: dotnet/android#6363

We were seeing JavaObjectTest.Dispose_Finalized() fail in a .NET 6
bump with $(UseInterpreter) set to true:

Expected: True
But was:  False
at Java.InteropTests.JavaObjectTest.Dispose_Finalized()
at System.Reflection.RuntimeMethodInfo.Invoke(Object , BindingFlags , Binder , Object[] , CultureInfo )

The first recommendation was to use a helper method from mono/mono's
unit tests:

https://github.com/mono/mono/blob/8266c5604b8c03882f2b06af27fdea46b142d6b9/mono/mini/TestHelpers.cs#L12

I removed usage of all System.Threading in JavaObjectTest in favor
of this helper method.

This did not solve this issue; we need to fix up the test to wait for
two GCs to complete:

FinalizerHelpers.PerformNoPinAction (() => {
    FinalizerHelpers.PerformNoPinAction (() => {
        var v     = new JavaDisposedObject (() => d = true, () => f = true);
        GC.KeepAlive (v);
    });
    JniEnvironment.Runtime.ValueManager.CollectPeers ();
});
JniEnvironment.Runtime.ValueManager.CollectPeers ();

With this change in place, the test now passes:

https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=5361266&view=ms.vss-test-web.build-test-results-tab

We can also remove the category added in d1d64c1.

[jonpryor]

@BrzVlad: Why is this member needed at all?

[jonpryor]

Answer: probably to prevent optimizing out the stackalloc: https://discord.com/channels/732297728826277939/732297837953679412/902261731471007765

[jonpryor]

This change somewhat confuses me: we need to call GC.Collect() from both a new thread and the main thread in order to get the test to pass? Instead of invoking GC.Collect() from the main thread twice?

This is very confusing to me.

[jonathanpeppers]

From what I understood a single call to FinalizerHelpers.PerformNoPinAction() ensures one GC.

And so we need two GCs for the finalizer to always run in this case. @BrzVlad is that correct?

Details here: dotnet/runtime#60638 (comment)

[BrzVlad]

The problem is that, if an object is alive then the GC will scan it and, by doing so, it will probably store it in the stack somewhere. In very unfortunate scenarios, at the second collection, the pinning step will find this reference existing on the stack and will pin the object (that might have now been dead otherwise). Because the JavaDisposedObject is alive during the first collection, we do this collection on a separate thread, so the second GC doesn't get to find this left over references on the stack.

[jonpryor]

work-in-progress commit message:

Context: https://github.com/xamarin/xamarin-android/pull/6363
Context: https://github.com/dotnet/runtime/issues/60638#issuecomment-949849104
Context: d1d64c10281eaa895fa415dfcafb8ed716a0db3c
Context: https://github.com/xamarin/xamarin-android/commit/c2c9ed47c94a03801986233ec9db860f0ef1daca

We were seeing `JavaObjectTest.Dispose_Finalized()` fail in a .NET 6
bump in xamarin-android with `$(UseInterpreter)` set to `true`:

	Expected: True
	But was:  False
	  at Java.InteropTests.JavaObjectTest.Dispose_Finalized()
	  at System.Reflection.RuntimeMethodInfo.Invoke(Object , BindingFlags , Binder , Object[] , CultureInfo )

The first recommendation was to use a helper method from mono/mono's
unit tests:

  * https://github.com/mono/mono/blob/8266c5604b8c03882f2b06af27fdea46b142d6b9/mono/mini/TestHelpers.cs#L12

I removed usage of all `System.Threading` in `JavaObjectTest` in
favor of this helper method.

This did not solve this issue; we need to fix up the test to wait for
two GCs to complete:

	FinalizerHelpers.PerformNoPinAction (() => {
	    FinalizerHelpers.PerformNoPinAction (() => {
	        var v     = new JavaDisposedObject (() => d = true, () => f = true);
	        GC.KeepAlive (v);
	    });
	    JniEnvironment.Runtime.ValueManager.CollectPeers ();
	});
	JniEnvironment.Runtime.ValueManager.CollectPeers ();

With this change in place, the test now passes:

  * https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=5361266&view=ms.vss-test-web.build-test-results-tab

We can also remove the category added in d1d64c10.