Don't auto subscribe to CAI for stylus handwriting

In [1] & [2] we introduce auto-subscription for editor bounds to IME. However,
it is actually better for IME to do it due to following reasons:
1. Simpler for IMEs do it. Easier state management in IME as to
   what is subscribed.
2. IME can subscribe to CusrosAnchorInfo as early as onStartInput(), which
   delivers required CAI even sooner to IME resulting in faster
   Handwriting startup.
3. We cannot predict what data IME may need. e.g. IME may not
   implement Rich handwriting gestures and hence may not need line
   bounds (Line bounds will be added in near future).

This CL essentially mechanically reverts [1] and a small part of [2]
No user observable behavior change.

[1] I3d6b1728d62139785593af14c24cb52bf2c91e31
[2] Ibba06e9a2533ca91c5cc215dfb18d21c9a74fb73

Fix: 238970465
Bug: 203086136
Bug: 210039666
Bug: 215533103
Test: atest CtsInputMethodTestCases
Change-Id: Ia72a9fe0ceac1798ee1989eaae3906e8e1b696bf