We had translated an uniform block only containing a large array member
into StructuredBuffer instead of cbuffer on D3D backend for slow fxc
compile performance issue with dynamic uniform indexing.
This patch throw a warning if a uniform block containing a large array
member fails to hit the optimization.

Bug: angleproject:3682
Change-Id: I33459b559923f16a8dfb70c6f46ec52f68d96e06
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2552365
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>