To support setting the custom `CurveMapping` to a well defined preset,
there exist a number of operators that are hardcoded to apply a
particular preset to a particular curve.
This commit begins to replace this functionality and make it part of the
template itself, allowing the preset to be applied to any curve. For
now, it only supports either positive or negative slopes, primarily for
the brush usecases.
The `brush.curve_preset` and `brush.sculpt_curves_falloff_preset`
operators are unneeded after this change and have been removed.
Notably, these preset controls have not been added elsewhere, they can
be added on a case by case basis in future commits by interested
modules.
Pull Request: https://projects.blender.org/blender/blender/pulls/146847
0f3c6da272