[Fuchsia] Synchronize image access in OutputPresenterFuchsia

Image access in OutputPresenterImages was not synchronized because
need_synchronization() was false int he images it uses.
Updated OutputPresenterFuchsia to set SCANOUT image usage bit and also
updated ExternalVkImageBacking::need_synchronization() to return true
for SCANOUT images. This ensures that image access in
OutputPresenterFuchsia properly.

Also fixed semaphore ownership handling in OutputPresenterFuchsia.

Bug: 1115692
Change-Id: Ibf375845eab2fbf320f777f45adcc98719ee239c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2353413


Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798127}