Improve draw performance of editor grids

[EVAST9919]

Performance difference is most noticeable with circular grid.

master	pr

Upon closer inspection you may see that grid alignment is slightly different. This is caused by the fact that grid line position may land between pixels and in that case grid isn't perfect as seen here (master)

Unfortunately, same issue occurs with this pr, but in different places, thus causing the visual difference and I'm not sure whether this can be fixed completely.

[EVAST9919]

Also there's an option to enable pixel snapping.
Enabling snapping helps to preserve overall clarity and looks much closer to the original look, but small blur caused by the linear filtering may help with aliasing a little.
So this one is up for debate.

master	pr	pr (+pixel snap)

[bdach]

I think this is okay. I wouldn't enable pixel snapping either because that is some really ugly aliasing on the screenshots provided.

The only caveat is that the draw overhead is basically moved to when the grid parameters are being updated, but that seems like a reasonable tradeoff.