If uniform block is translated to StructureBuffer on D3D backend,
must do a GPU-GPU copy when updating uniform buffer. If buffer's
latest usage is StructuredBuffer, directly upload to structured
buffer.

Bug: angleproject:3682
Change-Id: I7303866d08705a43238732e5f5ae4858f0a33d63
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2131871
Commit-Queue: Xinghua Cao <xinghua.cao@intel.com>
Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>