ContextVk's getTimestamp() and synchronizeCpuGpuTime() were the two
places that mCommandQueue was used outside of processing
SecondaryCommandBuffers. Migrating those functions to use the one-
off command buffer instead. This will allow for the removal of
mCommandQueue from ContextVk as we migrate it to RendererVk
instead for threading phase2 development.

Bug: b/154030730
Change-Id: Ic00ce56739dadcdc4b5a1b1839e0e18603bfe0eb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2209312Reviewed-by: Charlie Lao <cclao@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Tobin Ehlis <tobine@google.com>