Clean up requesting focus for SCVHs which aren't hosted inside windows

- Expose call on SCVH to request input focus when there is no
  associated host window (still only allowed for callers holding
  INTERNAL_SYSTEM_WINDOW)

Bug: 378565144
Flag: EXEMPT bugfix
Test: atest SurfaceControlViewHostTests
Change-Id: Ibd180775ec4121315597374ade5a24b439fe1881