Make sure view has focus before starting handwriting

It is possible for a view to have an active input connection without
having focus. If stylus movement occurs on a view in this state, the
view should be focused before starting handwriting.

Bug: 272522428
Test: atest android.view.stylus.HandwritingInitiatorTest
Change-Id: I1bf9ed46a747ccf42c7d1ca6ff271e7e4a20415f