Set SyncVk's SyncHelper to inherit from vk::Resource.

Bug: angleproject:2517
Change-Id: I499414d97e611d029abc12622f19436cbdb3e1f5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2160126
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>