Keymap: use both left/right modifier keys

Use both left/right modifier keys for:

- Fly Mode.
- Walk Mode.
- Area Split.
- Sculpt Detail Map.
- Sculpt Expand.
- Standard Modal Map

Resolves T98638.

source/blender/editors/screen/screen_ops.c

@@ -2490,6 +2490,7 @@ static int area_split_modal(bContext *C, wmOperator *op, const wmEvent *event)
       return OPERATOR_CANCELLED;
 
     case EVT_LEFTCTRLKEY:
+    case EVT_RIGHTCTRLKEY:
       sd->do_snap = event->val == KM_PRESS;
       update_factor = true;
       break;