Scribe in IMF: Automatically sub to CAI w/ Stylus 4/N

When Stylus handwriting mode is about to be used, automatically
subscribe IME to CursorAnchroInfo updates. This helps speed-up
stylus tasks in IME

Bug: 203086136
Bug: 210039666
Bug: 215533103
Test: atest CtsInputMethodTestCases
Change-Id: I3d6b1728d62139785593af14c24cb52bf2c91e31