PointVisualizer performance improvements

These are some low-hanging performance improvements for `PointVisualizer`.
In the long run, we might want to take a different approach altogether,
but these changes help some use cases that were previously impossible or
extremely slow.

1. Round to nearest pixel size, which has no visual change but stops us from producing thousands of usless canvases when using a sampled pixel size.
2. Fix a typo that was preventing proper caching when using outline colors.
3. Fix bad variable declaration in `EntityData` helper class.
4. Don't re-evaluate non-trivial constant values.
5. Add a fast-path for non-outlined points, which scales a larger texture instead of switching images.
Update CHANGES.md
Merge remote-tracking branch 'origin/master' into pointVisualizer-round
Merge remote-tracking branch 'origin/master' into pointVisualizer-round
Update CHANGES.md
Merge pull request #2262 from AnalyticalGraphicsInc/pointVisualizer-round

PointVisualizer performance improvements