HLSL: Partially address issue #463: accept GLSL layout(...).

This includes all "per variable" layout qualifiers, but the
key ones mattering and tested for now are:
  set=
  binding=
  constant_id=
  push_constant

hlsl/hlslTokens.h

@@ -64,6 +64,7 @@ enum EHlslTokenClass {
     EHTokIn,
     EHTokOut,
     EHTokInOut,
+    EHTokLayout,
 
     // template types
     EHTokBuffer,