Pointer Icon Refactor: Simplify tracking resolved pointer icon

There isn't a big benefit of tracking the pointer icon type and custom
icon individually in ViewRootImpl. It only adds complexity that is
already encapsulated in the PointerIcon class.

So we simplify the tracking logic by using a single mResolvedPointerIcon
member to track the resolved icon.

Bug: 293587049
Test: manual
Change-Id: I86e4929c01ed1322e8254c98bbf47949e8bc02ab