WIP: HLSL: add structuredbuffer pass by reference in fn params

This PR adds the ability to pass structuredbuffer types by reference
as function parameters.

It also changes the representation of structuredbuffers from anonymous
blocks with named members, to named blocks with pseudonymous members.
That should not be an externally visible change.

Test/hlsl.structbuffer.fn.frag

@@ -0,0 +1,23 @@
+
+StructuredBuffer<uint4>  sbuf : register(t10);
+RWStructuredBuffer<uint4> sbuf2;
+
+// Not shared, because of type difference.
+StructuredBuffer<uint3>  sbuf3 : register(t12);
+
+uint4 get(in StructuredBuffer<uint4> sb, uint bufferOffset)
+{
+    return sb[bufferOffset];
+}
+
+void set(in RWStructuredBuffer<uint4> sb, uint bufferOffset, uint4 data)
+{
+    sb[bufferOffset] = data;
+}
+
+float4 main(uint pos : FOO) : SV_Target0
+{
+    set(sbuf2, 2, get(sbuf, 3));
+
+    return 0;
+}