[TrimmableTypeMap] Add GetStaticMethodFallbackTypesCore override for desugared default interface methods

[simonrozsival]

Part of #10788

Problem

TrimmableTypeMapTypeManager does not override GetStaticMethodFallbackTypesCore(). The legacy ManagedTypeManager overrides this to support Java 8+ default interface methods that are desugared by D8/R8:

// ManagedTypeManager.cs:155-166
protected override IReadOnlyList<string>? GetStaticMethodFallbackTypesCore(string jniSimpleReference)
{
    int slash = jniSimpleReference.LastIndexOf('/');
    var desugarType = slash > 0
        ? $"{jniSimpleReference.Substring(0, slash + 1)}Desugar{jniSimpleReference.Substring(slash + 1)}"
        : $"Desugar{jniSimpleReference}";
    return new[] {
        $"{desugarType}$_CC",
        $"{jniSimpleReference}$-CC",
    };
}

Without this, calls to desugared default interface methods will fail with NoSuchMethodError at runtime when using the trimmable type map.

Fix

Add the same override to TrimmableTypeMapTypeManager. This is a 1-line method copy.

Impact

Any app using Java libraries with default interface methods (Java 8+ feature, very common in modern Android libraries like AndroidX) could be affected.