HLSL: Add typedef grammar and production.

Test/hlsl.typedef.frag

@@ -0,0 +1,11 @@
+typedef float4 myVec4;
+
+float4 ShaderFunction(float4 input, int ii) : COLOR0
+{
+    typedef int myInt;
+    myVec4 a1 = myVec4(1.0);
+    myInt i = 2;
+    typedef myInt myInt2;
+    myInt2 j = ii;
+    return input * a1 + myVec4(i + j);
+}