Layer adjustments

[bhousel]

This adjusts the stacking order so that the interactive OSM objects take precedence over the interactive non-OSM objects.

fixes #5257

Still need to test a bit more..

[bhousel]

This is good enough for now.

I did also attempt to remove the supersurface and instead set separate transforms for each layer, but doing it that way ended up being worse for performance.

If each layer could have a separate transform, they could render during async idle callback, instead of all together on the main thread.

I dug a bit into performance and there are big issues with style recalculation and repainting that I have no idea how to fix. 😞

[iandees]

Maybe it's ...