[generator] Add support for skipInterfaceMethods.

[jpobst]

Context: #1264

The scenario described in #1264 seems very complex to fix, as we would have to determine if each interface method has a compatible DIM on any other interface in scope.

As a workaround, we can mimic skipInvokerMethods with a new skipInterfaceMethods metadata that allows us to suppress generation of an abstract method in an abstract class that implements the interface.

The example in #1264 would be fixed with:

<attr
  path="/api/package[@name='kotlin.collections']/class[@name='AbstractList']"
  name="skipInterfaceMethods">
    java/util/SequencedCollection.reversed()Ljava/util/SequencedCollection;
</attr>

The format is the same as skipInvokerMethods.

[jonpryor]

Context: https://github.com/dotnet/java-interop/issues/1264
Context: 73ebad2496a0d6df251fd24e216248da70e3fea9
Context: a7e09b7be4dc9dbc1c1a65b5f2c1e8fcf028b209
Context: https://github.com/dotnet/android/commit/00256b6912f80e36c2a5d31046eb8c32691ed221

Consider [`java.util.List<E>`][0], which implements
[`java.util.SequencedCollection<E>`][1] and provides an interface
default method to implement `SequencedCollection<E>.reversed()`:

	// Java
	package java.util;
	public /* partial */ interface SequencedCollection<E> implements Collection<T> {
	  SequencedCollection<E> reverse ();
	}
	public /* partial */ interface List<E> implements SequencedCollection<E> {
	  default List<E> reversed() { … }
	}

We then *bind* the above, along with some manual fixups in
dotnet/android@00256b69:

	// C# bindings
	public partial interface ISequencedCollection {
	  [Register ("reversed", "()Ljava/util/SequencedCollection;", "GetReversedHandler:Java.Util.ISequencedCollectionInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null", ApiSince = 35)]
	  ISequencedCollection? Reversed ();
	}

	public partial interface IList : ISequencedCollection {
	  [Register ("reversed", "()Ljava/util/List;", "GetReversedHandler:Java.Util.IList, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null", ApiSince = 35)]
	  unsafe Java.Util.ISequencedCollection Java.Util.ISequencedCollection.Reversed () => …
	}

Next, we try to bind [androidx.paging:paging-common-android][2].
The [`androidx.paging.ItemSnapshotList`][3] inherits from
[`kotlin.collections.AbstractList`][4]:

	// Kotlin
	package kotlin.collections;
	public abstract /* partial */ class AbstractList<out E> protected constructor() :
	  kotlin.collections.AbstractCollection<E>(), java.util.List<E> {
	}

In a scenario that rhymes with 73ebad24, `generator` with
`Mono.Android.dll` (bindings for `Java.Util.IList`) cannot determine
that the `Kotlin.Collections.AbstractList` type has a `Reversed()`
method (via `Java.Util.IList`), and so re-declares it:

	// C#
	public partial class AbstractList : Kotlin.Collections.AbstractCollection, Java.Util.IList {
	  public abstract ISequencedCollection Reversed ();
	}

We fear that a complete fix for this may be complicated, as we would
have to determine if each interface method has a compatible default
interface method on any other interface in scope.

Introduce a new `skipInterfaceMethods` metadata, with identical
semantics to `skipInvokerMethods` (73ebad24), to allow specifying
`interface`-derived methods which should be *skipped* when generating
bindings:

	<attr
	    path="/api/package[@name='kotlin.collections']/class[@name='AbstractList']"
	    name="skipInterfaceMethods">
	  java/util/SequencedCollection.reversed()Ljava/util/SequencedCollection;
	</attr>

The above fragment would prevent `Reversed()` from being declared in
the binding for `Kotlin.Collections.AbstractList`.

[0]: https://developer.android.com/reference/java/util/List
[1]: https://developer.android.com/reference/java/util/SequencedCollection
[2]: https://maven.google.com/web/index.html?q=paging#androidx.paging:paging-common-android
[3]: https://developer.android.com/reference/androidx/paging/ItemSnapshotList
[4]: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-abstract-list/