This commit doesn't implement any new feature but makes the new curves
object type no longer experimental.

Documentation:

• https://docs.blender.org/manual/en/3.3/modeling/curves/primitives.html#empty-hair
• https://docs.blender.org/manual/en/3.3/sculpt_paint/curves_sculpting/introduction.html

Note: This also makes the Selection Paint tool available. This tool
should have been moved out of the "New Curves Tool" flag when we got the
selection drawing to work.