HLSL: add test coverage for sub-vec4 texture intrinsics

This changes no functional code.  There was a bit of a testing hole
in that textures templatized on sub-vec4 types were not being exercised
with any intrinsics.  This adds some basic sanity coverage of that case.

Test/hlsl.texture.subvec4.frag

@@ -0,0 +1,41 @@
+
+Texture2DMS <float>  g_tTex2dmsf1;
+Texture2DMS <float2> g_tTex2dmsf2;
+Texture2DMS <float3> g_tTex2dmsf3;
+Texture2DMS <float4> g_tTex2dmsf4;
+
+Texture2D <float>  g_tTex2df1;
+Texture2D <float2> g_tTex2df2;
+Texture2D <float3> g_tTex2df3;
+Texture2D <float4> g_tTex2df4;
+
+SamplerState g_sSamp;
+
+float4 main()
+{
+    uint MipLevel;
+    uint WidthU;
+    uint HeightU;
+    uint ElementsU;
+    uint DepthU;
+    uint NumberOfLevelsU;
+    uint NumberOfSamplesU;
+
+    g_tTex2dmsf1 . GetDimensions(WidthU, HeightU, NumberOfSamplesU);
+    g_tTex2dmsf2 . GetDimensions(WidthU, HeightU, NumberOfSamplesU);
+    g_tTex2dmsf3 . GetDimensions(WidthU, HeightU, NumberOfSamplesU);
+    g_tTex2dmsf4 . GetDimensions(WidthU, HeightU, NumberOfSamplesU);
+
+    g_tTex2dmsf1 . Load(int2(1,2), 3);
+    g_tTex2dmsf2 . Load(int2(1,2), 3);
+    g_tTex2dmsf3 . Load(int2(1,2), 3);
+    g_tTex2dmsf4 . Load(int2(1,2), 3);
+
+    g_tTex2df1 . Sample(g_sSamp, float2(.1, .2));
+    g_tTex2df2 . Sample(g_sSamp, float2(.1, .2));
+    g_tTex2df3 . Sample(g_sSamp, float2(.1, .2));
+    g_tTex2df4 . Sample(g_sSamp, float2(.1, .2));
+    
+    return 0;
+}
+