HLSL: Add ConstantBuffer<T> syntax

Note: multi-dimension arrays of ConstantBuffer objects will go through uniform flattening.

Test/hlsl.constantbuffer.frag

@@ -0,0 +1,26 @@
+
+struct c1_t {
+    float4 x;
+};
+
+struct c2_t {
+    bool x;
+    float y;
+};
+
+ConstantBuffer<c1_t> cb1 : register(b12);
+ConstantBuffer<c2_t> cb2[3];
+ConstantBuffer<c2_t> cb3[2][4];
+
+cbuffer cbuff {
+    int c1;
+};
+
+float4 main() : SV_Target0
+{
+    if (cb3[1][2].x)
+        return cb1.x + cb2[1].y + c1;
+    else
+        return cb3[2][3].y;
+}
+