WIP: HLSL: add ability to pass struct buffers with counters to fns

This modifies function parameter passing to pass the counter
buffer associated with a struct buffer to a function as a
hidden parameter.  Similarly function declarations will have
hidden parameters added to accept the associated counter buffers.

There is a limitation: if a SB type may or may not have an associated
counter, passing it as a function parameter will assume that it does, and
the counter will appear in the linkage whether or not there is a counter
method used on the object.

gtests/Hlsl.FromFile.cpp

@@ -255,6 +255,7 @@ INSTANTIATE_TEST_CASE_P(
         {"hlsl.structarray.flatten.geom", "main"},
         {"hlsl.structbuffer.frag", "main"},
         {"hlsl.structbuffer.append.frag", "main"},
+        {"hlsl.structbuffer.append.fn.frag", "main"},
         {"hlsl.structbuffer.atomics.frag", "main"},
         {"hlsl.structbuffer.byte.frag", "main"},
         {"hlsl.structbuffer.coherent.frag", "main"},