Refactor InkWindow lifetime

Refactor InkWindow instance to live longer with a timer.
This should help with faster handwritiing intiiaiton if handwriting is
intiiated again shortly after the new window gets bound to IME.

Also refactored to finish handwriting on idle timeout rather than just
removing the window.

Bug: 291946496
Test: atest StylusHandwritingTest
Change-Id: I29a1eec9502b9558f8a7992308ec894f160dd4b7