HLSL: phase 1: add RWTexture and RWBuffer

There's a lot to do for RWTexture and RWBuffer, so it will be broken up into
several PRs.  This is #1.

This adds RWTexture and RWBuffer support, with the following limitations:
  * Only 4 component formats supported
  * No operator[] yet

Those will be added in other PRs.

This PR supports declarations and the Load & GetDimensions methods.  New tests are
added.

hlsl/hlslTokens.h

@@ -209,6 +209,13 @@ enum EHlslTokenClass {
     EHTokTextureCubearray,
     EHTokTexture2DMS,
     EHTokTexture2DMSarray,
+    EHTokRWTexture1d,
+    EHTokRWTexture1darray,
+    EHTokRWTexture2d,
+    EHTokRWTexture2darray,
+    EHTokRWTexture3d,
+    EHTokRWBuffer,
+    
 
     // variable, user type, ...
     EHTokIdentifier,