autofill: pass keyevent from fillui to app

Since autofill window was made to have window focus, app lost the
ability to accept physical keyboard typing. User can no longer
type on physical keyboard to filter autofill result.

This CL dispatches unhandled keyevent(e.g. A/B/C) from autofill
window to app ViewRootImpl in a similar way InputMethodService
dispatches keyevent to app's ViewRoot.

The unhandled key is sent to app window's ViewRootImpl
PreImeStage so that the keystroke could be translated to CJK by IME.

This CL does not affect fullscreen autofill window for TV  where app
window is fully covered: user has to close fullscreen autofill window
first.

Bug: 72951156
Test: atest CtsAutoFillServiceTestCases:LoginActivityTest

Change-Id: I8e50cfdfe8d5691d2b248d85f924c38488ca30f4