pointer input: handle warp events differently from absolute motion events

As Wayland doesn't have a warp event yet, before this commit, warps were
dealt with like normal absolute motion events. This trips up games though,
which don't deal with actual absolute motion events well. As a solution
to that, until an actual warp event is a thing, we send a motion event with
a position + a relative motion event with no motion

BUG: 458233
CCBUG: 482476
(cherry picked from commit 630ba5fa)