When the asset view in the sidebar of the pose library would contain more than a few handful poses, interaction and animation playback performance would be impacted considerably. This was because our icon drawing scales image buffers using a rather slow method on the CPU. This commit changes it so the asset icons are scaled using the GPU. Note that this is a temporary change. I'd like all icon code to use GPU-side scaling, see D13144. But such a change is too risky to do in the release branch at this point, so this fix is specifically for the 3.0 release.