WIP: HLSL: Add GS support

This PR adds:

[maxvertexcount(n)] attributes

point/line/triangle/lineadj/triangleadj qualifiers

PointStream/LineStream/TriangleStream templatized types

Append method on above template types

RestartStrip method on above template types.

Test/hlsl.basic.geom

@@ -0,0 +1,25 @@
+struct PSInput
+{
+    float  myfloat    : SOME_SEMANTIC;
+    int    something  : ANOTHER_SEMANTIC;
+};
+
+struct nametest {
+    int Append;        // these are valid names even though they are also method names.
+    int RestartStrip;  // ...
+};
+
+[maxvertexcount(4)]
+void main(triangle in uint VertexID[3] : VertexID,
+          triangle uint test[3] : FOO, 
+          inout LineStream<PSInput> OutputStream)
+{
+    PSInput Vert;
+
+    Vert.myfloat    = test[0] + test[1] + test[2];
+    Vert.something  = VertexID[0];
+
+    OutputStream.Append(Vert);
+    OutputStream.Append(Vert);
+    OutputStream.RestartStrip();
+}