HLSL: Fix 1201: Accept 'layout' as an identifier.

Test/hlsl.layout.frag

@@ -14,5 +14,6 @@ tbuffer tbufName2 : layout(set=4,binding=7) {
 
 float4 PixelShaderFunction(float4 input) : COLOR0
 {
-    return input + v1 + v5 + v1PostLayout;
+    float4 layout = 2.0;
+    return input + v1 + v5 + v1PostLayout * layout;
 }

hlsl/hlslGrammar.cpp

@@ -4077,6 +4077,7 @@ const char* HlslGrammar::getTypeString(EHlslTokenClass tokenClass) const
     case EHTokMin16int:   return "min16int";
     case EHTokMin12int:   return "min12int";
     case EHTokConstantBuffer: return "ConstantBuffer";
+    case EHTokLayout:     return "layout";
     default:
         return nullptr;
     }