Provide layer IDs to Java InputWindowHandle.

This allows us to uniquely identify layers such as surface views in
addition to those views that are backed by window tokens.

Bug: 404617897
Test: Build; unit test; atest RenderSessionService test with plumbing
Flag: EXEMPT internal plumbing
Change-Id: I7749671aaea684527f80161ec401a2f36678f3d7