Curves: Interpolate point count in add brush

This commit adds an option to interpolate the number of control points
in new curves based on the count in neighboring existing curves. The
idea is to provide a more automatic default than manually controlling
the number of points in a curve, so users don't have to think about
the resolution quite as much.

Internally, some utilities for creating new curves are extracted to a
new header file. These can be used for the various nodes and operators
that create new curves.

The top-bar UI will be adjusted in a separate patch, probably moving
all of the settings that affect the size and shape of the new curves
into a popover.

Differential Revision: https://developer.blender.org/D14877

release/scripts/startup/bl_ui/space_view3d.py

@@ -523,6 +523,7 @@ class _draw_tool_settings_context_mode:
             layout.prop(brush.curves_sculpt_settings, "curve_length")
             layout.prop(brush.curves_sculpt_settings, "interpolate_length")
             layout.prop(brush.curves_sculpt_settings, "interpolate_shape")
+            layout.prop(brush.curves_sculpt_settings, "interpolate_point_count")
 
         if brush.curves_sculpt_tool == 'GROW_SHRINK':
             layout.prop(brush, "direction", expand=True, text="")