HLSL: implement TextureBuffer<type>

Almost equivalent to tbuffer, except members not at global scope.
So, reference is "TextureBuffer_var.member", not simply "member".

Test/hlsl.texturebuffer.frag

@@ -0,0 +1,17 @@
+
+struct Data {
+    float4  f;
+    int4    i;
+};
+
+TextureBuffer<Data> TextureBuffer_var : register(t0);
+
+tbuffer tbuf2 {
+    float4 f2;
+    int4   i2;
+};
+
+float4 main(float4 pos : SV_POSITION) : SV_TARGET
+{
+    return TextureBuffer_var.f + f2;
+}