Extend Foliage Spawner Density Control

[Mr4Goosey]

It'd be incredibly useful if foliage had their own "layer" system, like non-weightmapped layers on Landscapes; they don't contribute to the material in any meaningful way, they're simply there to control foliage densities.

By extension it'd also be neat to have a proper Voxel Graph integration, where you can specify a graph to control spawning, making it easier to have complex equations and conditions to control foliage spawning. Not your WORLD's graph, it's own graph.

[Notion7]

The actor cutoff at a certain level in voxel spawner actors is great. But what would be amazing is if we could set alternate actors to use instead at certain heights. So for example, while sculpting underground caves, all the data used to place regular actors could be utilized for the placement of underground actors, without having to calculate new stuff for new actors

[Notion7]

when removing foliage via UV, about 5% of it persists no matter the distance or angle I paint at. For trees, I sometimes have to 'paint up the trunk' closer to the center of mass to get it to remove (even though their pivots are on the ground). So I am thinking maybe some of the actors are too low or high to be affected by the paint. Just an example here, I can never remove these:

[Notion7]

looks like this debug arrow is staying even after unchecking debug

[deanvaessen]

Adding a comment that I likewise find this'd an exciting addition to the foliage system.