Fix missing subitem indicator when menu items in the Customizer are children of parent menu items & add menu item original title to button text. Adds parity with the admin menu editor and fixes a bug where the button text was 'untitled' if the menu item title had not been edited.
Props designsimply, afercia, celloexpressions, kushang78, joedolson, rcreators.
Fixes#32728.
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