perf(SprayBrush): enhance perf using new Group

[ShaMan123]

This PR is an excellent demonstration of the power of the new Group and what can be unlocked using it
control
perf

Basically it reduces computation cost by iterating only once over the spray dots instead of a number of times.
It split up the dots into a number of groups that act as buffers to cut down iterations.
I need to get these buffers to render cache once they're maxed out and then performance will rise even more (splitting the rendering of the entire spray into smaller chunks and then at mouseup the create path is a group of groups that have already been cached so overhead will be minimal)

Will merge once v6! stabilizes

The buffering approach can/should be used by canvas for perf

If we wrap the result of the spray brush with another group we enhance perf even more in case it is used with clip path or in other cases that invalidate cache.

In action

You'll see that the dots double every second or so. That's the buffering group.
Notice that normally there is a massive frame drop on mouse up and here, even though the spray is huge there is no visible drop.

Zoom in on mouse up

spray1.mp4