[Editor] Set the creation method for free highlights to 'main_toolbar' (bug 1883394)

src/display/editor/highlight.js

@@ -727,6 +727,7 @@ class HighlightEditor extends AnnotationEditor {
         highlightId: this._freeHighlightId,
         highlightOutlines: this._freeHighlight.getOutlines(),
         clipPathId: this._freeHighlightClipId,
+        methodOfCreation: "main_toolbar",
       });
     } else {
       parent.drawLayer.removeFreeHighlight(this._freeHighlightId);