This change propagates the storage qualifier from the buffer object to its contained
array type so that isStructBufferType() realizes it is one.  That propagation was
happening before only for global variable declarations, so compilation defects would
result if the use of a function parameter happened before a global declaration.

This fixes that case, whether or not there ever is a global declaration, and
regardless of the relative order.

This changes the hlsl.structbuffer.fn.frag test to exercise the alternate order.

There are no differences to generated SPIR-V for the cases which successfully compiled before.