Vulkan mandates that vertex buffer offsets are within the size of the
buffer even if robust buffer access is enabled. Do a check in
VertexArrayVk::syncDirtyAttrib to guard against this.

Bug: angleproject:3350
Change-Id: Ia01deb9b7335dd8f632f2cf9b32d2908ba55645c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2044491
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>