Fix broken toolbar drag/drop behavior in dropzones

[kenneth-marut-work]

What it does

Fixes #12256 by adding an onDragOver attribute to the toolbar's dropzones which points to the existing handleOnDragEnter handler. The addition of the lines below from #12065 in frontend-application.ts seem to have overridden the existing onDragEnter handler

How to test

Build this branch and try dragging a toolbar item in the toolbar's dropzones which can be found on the left/right sides of each toolbar column

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[colin-grant-work]

This reenables dropping on empty space in the toolbar. 👍