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.
Now we add more conditions to restrict the translation. Only indexing
operator is allowed to operate on this uniform block variable. And we
also restrict the types of uniform block's member.

Bug: angleproject:3682
Change-Id: I992b7890d84fcaa6169722af6d7e14785526d48a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2351728
Commit-Queue: Xinghua Cao <xinghua.cao@intel.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>