Paint: Ignore inbetween events for anchored strokes

When using anchored strokes, inbetween events are not needed since there
is no stroke path to be reconstructed. Handling the inbewteen events are
only producing unnecessary updates, creating performance issues.

Reviewed By: sergey, brecht

Differential Revision: https://developer.blender.org/D9053

source/blender/editors/sculpt_paint/paint_stroke.c

@@ -257,6 +257,10 @@ static bool paint_stroke_use_scene_spacing(Brush *brush, ePaintMode mode)
 
 static bool paint_tool_require_inbetween_mouse_events(Brush *brush, ePaintMode mode)
 {
+  if (brush->flag & BRUSH_ANCHORED) {
+    return false;
+  }
+
   switch (mode) {
     case PAINT_MODE_SCULPT:
       if (ELEM(brush->sculpt_tool,