Replace mip selection with sample idx when viewing Tex2DMS. Refs #79

* Also for float/unorm texture add an additional "resolved" option that
  just does an unweighted average of all samples, which is the behaviour
  from before (assuming that's what ResolveSubresource does).

renderdoccmd/renderdoccmd_win32.cpp

@@ -239,6 +239,7 @@ void DisplayRendererPreview(ReplayRenderer *renderer)
 			TextureDisplay d;
 			d.texid = texs[i].ID;
 			d.mip = 0;
+			d.sampleIdx = ~0U;
 			d.overlay = eTexOverlay_None;
 			d.CustomShader = ResourceId();
 			d.HDRMul = -1.0f;