Introduce TextBoundsInfo

This is an API for IME to request text bounds information from editor to
perform handwriting rich gestures. It's useful for IMEs to create custom
handwriting gesture that's not supported the HandwritingGesture. And
it can also be used to provide default rich gesture implementation for
handwriting gesture compatibility.

Bug: 239843501
Test: atest TextBoundsInfoTest
Change-Id: Ia7522371976a4e1fcdff4cc0d244ea427ad3d7c9