Globally enable stylus hover icon

Requested by Scribe UX, a hover icon should be displayed for editors
that support scribe handwriting. But no hover icon should be displayed
for other views.
To achieve the goal, this CL enables the stylus hover icon globally so
that WebView and other toolkits can support hover icon via overriding
View#onResolvePointerIcon for stylus. And it also hide the stylus hover
icon for views that support PointerIcon for mouse.
We want to preserve the existing behavior for devices that
move the mouse cursor. And for devices that don't, like a
hovering stylus, we defer to the default behavior in View.java.

Bug: 277951386
Test: atest PointerIconTest
Change-Id: Ic8b2bfc7c3fb5ac2954381a373ba0f73790bbe15