Introduce handwriting hover icon and update its hide/show logic

Updated the hover icon for PointerIcon.TYPE_HANDWRITING. And also
updated the hide/show logic of the handwriting hover icon.
By default handwriting hover icon is displayed for areas where
handwriting is available.
Now the hover icon will hide after handwriting is triggered on the
active editor until one of the following events happens:
a) stylus clicks something.
b) stylus hovers on another editor that supports handwriting.
c) the current focused editor lost focus.

The hotspot of the pointer icon is designed to be
x: 34% of the width; 8.25 dp (rouneded to the closest quarter-dp).
y: 100% of height, which is set to 23.75dp because
hotSpotY must be less than bitmap height.

Bug: 274696514
Test: atest HandwritingInitiatorTest
Change-Id: I9270076fc3f5eae78386fb5c2e15f9872ddf0c40