EXO: Move GetTargetSurfaceForLocatedEvent out of ShellSurfaceBase

Moved GetTargetSurfaceForLocatedEvent out of shell_surface_base and
into shell_surface_util. This is needed so cast can use this function
for touch events in exo.

Bug: 896710
Test: Run exo_unittests
Change-Id: Ifa8f6219ffa54a349922eb78f51a56dda953191c
Reviewed-on: https://chromium-review.googlesource.com/c/1334557
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613710}
7 files changed