WIP: HLSL: Support InputPatch variables in patch constant functions

Previously, patch constant functions only accepted OutputPatch.  This
adds InputPatch support, via a pseudo-builtin variable type, so that
the patch can be tracked clear through from the qualifier.

gtests/Hlsl.FromFile.cpp

@@ -129,6 +129,7 @@ INSTANTIATE_TEST_CASE_P(
         {"hlsl.hull.2.tesc", "main"},
         {"hlsl.hull.void.tesc", "main"},
         {"hlsl.hull.ctrlpt-1.tesc", "main"},
+        {"hlsl.hull.ctrlpt-2.tesc", "main"},
         {"hlsl.identifier.sample.frag", "main"},
         {"hlsl.if.frag", "PixelShaderFunction"},
         {"hlsl.implicitBool.frag", "main"},