Fix curves sculpting Selection Paint missing refresh

This was reported as part of D15219 but it is a problem in master, not
in the patch.

EEVEE is drawing with a cheap sampling when navigating or painting, but
we need to clear the painting flag when we are done painting.

For a rainy day: DRW_state_is_navigating() should be renamed to indicate
that it also checks for the painting flag.

source/blender/editors/sculpt_paint/curves_sculpt_intern.hh

@@ -111,7 +111,7 @@ class CurvesSculptCommonContext {
   const Scene *scene = nullptr;
   ARegion *region = nullptr;
   const View3D *v3d = nullptr;
-  const RegionView3D *rv3d = nullptr;
+  RegionView3D *rv3d = nullptr;
 
   CurvesSculptCommonContext(const bContext &C);
 };

source/blender/editors/sculpt_paint/curves_sculpt_selection_paint.cc

@@ -140,6 +140,7 @@ struct SelectionPaintOperationExecutor {
      * selection is handled as a generic attribute for now. */
     DEG_id_tag_update(&curves_id_->id, ID_RECALC_GEOMETRY);
     WM_main_add_notifier(NC_GEOM | ND_DATA, &curves_id_->id);
+    ctx_.rv3d->rflag &= ~RV3D_PAINTING;
     ED_region_tag_redraw(ctx_.region);
   }