Blender Git Loki

View3D: Cursor Snap Refactor

Make the snap system consistent with the placement tool and leak-safe.

**Changes:**
- Store `SnapCursorDataIntern` in a `static` variable;
- Initialize (lazily) `SnapCursorDataIntern` only once (for the keymap).
- Move setup members of `V3DSnapCursorData` to a new struct `V3DSnapCursorState`
- Merge `ED_view3d_cursor_snap_activate_point` and `ED_view3d_cursor_snap_activate_plane` into `state = ED_view3d_cursor_snap_active()`
- Merge `ED_view3d_cursor_snap_deactivate_point` and `ED_view3d_cursor_snap_deactivate_plane` into `ED_view3d_cursor_snap_deactive(state)`
- Be sure to free the snap context when closing via `ED_view3d_cursor_snap_exit`
- Use RNA properties callbacks to update the properties of the `"Add Primitive Object"` operator