HLSL: allow multi-dimensional arrays

All the underpinnings are there; this just parses multiple array dimensions
and passes them through to the existing mechanisms.

Also, minor comment fixes, and add a new test for multi-dim arrays.

gtests/Hlsl.FromFile.cpp

@@ -83,6 +83,7 @@ INSTANTIATE_TEST_CASE_P(
         {"hlsl.amend.frag", "f1"},
         {"hlsl.array.frag", "PixelShaderFunction"},
         {"hlsl.array.implicit-size.frag", "PixelShaderFunction"},
+        {"hlsl.array.multidim.frag", "main"},
         {"hlsl.assoc.frag", "PixelShaderFunction"},
         {"hlsl.attribute.frag", "PixelShaderFunction"},
         {"hlsl.buffer.frag", "PixelShaderFunction"},