Introduce Scribe Rich gestures API

During a stylus handwriting session, user can perform a
stylus gesture operation like  Select, delete, insert on an
area of text. IME needs APIs to perform these gestures on text.
This CL introduces API signature for Select, delete, insert gestures.

Design doc: go/scribe-gestures-api

Bug: 239783077
Bug: 210039666
Test: Manually build & compile HandwritingIme

Change-Id: I53bcb62e03ac1c371feb60d1385c88c921754092