Fix: Curves sculpt mode keymaps missing in preferences

These changes make the curves sculpt mode keymap consistent
with other modes. They now show up in the keymap, for potential
editing of tool shortcuts, etc. I don't fully understand this system,
but at least these changes should make it consistent.

Differential Revision: https://developer.blender.org/D15112

release/scripts/modules/bl_keymap_utils/keymap_hierarchy.py

@@ -88,6 +88,10 @@ _km_hierarchy = [
             _km_expand_from_toolsystem('VIEW_3D', 'SCULPT'),
         ]),
 
+        ('Sculpt Curves', 'EMPTY', 'WINDOW', [
+            _km_expand_from_toolsystem('VIEW_3D', 'CURVES_SCULPT'),
+        ]),
+
         ('Particle', 'EMPTY', 'WINDOW', [
             _km_expand_from_toolsystem('VIEW_3D', 'PARTICLE'),
         ]),