HLSL: matrix swizzle (_12, _m23) syntax, partial semantics.

This partially addressess issue #670, for when the matrix swizzle
degenerates to a component or column: m[c], m[c][r] (where HLSL
swaps rows and columns for user's view).

An error message is given for the arbitrary cases not covered.

These cases will work for arbitrary use of l-values.

Future work will handle more arbitrary swizzles, which might
not work as arbitrary l-values.

gtests/Hlsl.FromFile.cpp

@@ -154,6 +154,7 @@ INSTANTIATE_TEST_CASE_P(
         {"hlsl.logical.binary.frag", "main"},
         {"hlsl.logical.binary.vec.frag", "main"},
         {"hlsl.matNx1.frag", "main"},
+        {"hlsl.matrixSwizzle.vert", "ShaderFunction"},
         {"hlsl.mintypes.frag", "main"},
         {"hlsl.multiEntry.vert", "RealEntrypoint"},
         {"hlsl.multiReturn.frag", "main"},