This commit adds a "soft" selection to curve control points,
a sculpt tool to paint the selection, and uses the selection influence
in the existing sculpt brushes.
The selection is the inverse of the "mask" from mesh sculpt mode
currently. That change is described in more detail here: T97903
{F13090312 size=full}
Since some sculpt tools are really "per curve" tools, they use the average
point selection of all of their points. The delete brush considers a curve
selected if any of its points have a non-zero selection.
There is a new option to choose the selection domain, which affects how
painting the selection works. You can also turn the selection off by clicking
on the active domain.
The main limitation currently is that we can't see the values in the viewport at all.
However, I made a file with some geometry nodes and shader nodes to visualize
the behavior. The only difference is that sometimes the layers are removed as an
optimization, so it looks unselected when it really is.
{F13090309}
Todo:
* Make attributes starting with `.` inaccessible in geometry nodes (as per T97452).