As pointed out in ppy#16435, beatmaps
with too many control points (usually added via external automation
apps) could cause the lazer editor to grind to a halt.

The overheads here are mostly from the GL side. An eventual goal would
be to render this in a smarter way, rather than using thousands of
drawables. Until that, this optimisation should help reduce the overhead
by omitting control points in close proximity that are redundant for
display purposes.

I've tried to contain this in the display logic directly, with the goal
that it can be ripped out as fast as it was added. Certainly required
more changes than I hoped for, but I don't think it's too ugly.

…the timeline