Implements the design from #120318. The existing selection nodes now have
the ability to deal with float/soft selection. For meshes the soft selection
corresponds to the inverse of the sculpt mask attribute. In the future this
will likely be unified with edit mode selection a bit more which is why
this design was chosen compared to separating masking and selection.
Curves and point clouds already use a single selection attribute with
either data type.
Pull Request: https://projects.blender.org/blender/blender/pulls/126316
98f0926825