Cleanup: Use enum type for brush type switch

This way we'll get a compiler warning when a new brush type is added,
and not handled in the switch. Plus a runtime warning when an invalid
value is cast to the enum. Both can help catching errors.

source/blender/blenkernel/intern/paint.cc

@@ -789,13 +789,17 @@ static void paint_brush_default_essentials_name_get(
       name = "Pencil";
       /* Different default brush for some brush types. */
       if (brush_type) {
-        switch (*brush_type) {
+        switch (eBrushGPaintType(*brush_type)) {
           case GPAINT_BRUSH_TYPE_ERASE:
             name = "Eraser Hard";
             break;
           case GPAINT_BRUSH_TYPE_FILL:
             name = "Fill Area";
             break;
+          case GPAINT_BRUSH_TYPE_DRAW:
+          case GPAINT_BRUSH_TYPE_TINT:
+            /* Use default, don't override. */
+            break;
         }
       }
       eraser_name = "Eraser Soft";