EGL_KHR_fence_sync introduces the EGLSync object and associated
create/destroy/clientWait functions.  EGL_KHR_wait_sync adds the
serverWait function on top of that.

Bug: angleproject:2466
Change-Id: Iebb239a85c4471ea18b3c3a8a83b793af555e31d
Reviewed-on: https://chromium-review.googlesource.com/c/1412261
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>