Load correct resources for pointer icon on external screen

When mouse pointer changes displays, it should also reload the
icon from new resources. Otherwise, if the densities of the
previous and new displays are different, the size of the pointer
sprite will look too small or too large.

- Add getDisplayContext to get the corresponding Context by displayId.
- Cache system pointer icons per display, clear if display removed.
- Fix icon moved to default when not resetting out of task bound.

Bug: 113559891
Test: Enable mouse pointer on default display, move to other screen
Change-Id: Ic42d0ec32d9c979281e13c83b9e8b57134fd4f0d