Fix glitch in Studio Modeler - multiple display of same value in widget type selection

As shown in the attached sreen copy, a glitch in the display of a layout widget filter makes a selection appear mutliple times

To reproduce, in a browser (FF and Chrome at least), look at https://connect.nuxeo.com/nuxeo/site/studio/ide?project=pabgrall-SANDBOX#@feature:SUP23607.contentView =>

• Edit the Path(MyDoc), and in the Layout Widget Editor, click on the widget type "Path tree" and hit Save
• Edit the Path(MyDoc), and in the Layout Widget Editor, click on the widget type "Path tree" and hit Save a second time
• Edit the Path(MyDoc), and in the Layout Widget Editor, click on the widget type "Path tree" and hit Save a third time (you already see twice "Path tree", "Localized vocabulary tree", "Rendition Names selection" and "Tags selection")
• Edit the Path(MyDoc), and in the Layout Widget Editor, click on the widget type "Path tree" and hit Save a fourth time => 3 times the values
  ...