WM: Clean up InputTarget interface

Cherry-pick of changes in I21a6f1a7353844d2b0f59f32e802ed1f0a3d66ff
that didnt land in master.

Bug: b/188792659
Test: presubmit
Test: test talkback
Change-Id: Ia799e6104ceba66f4b7fabb3e151536d9d168169
5 files changed