App menu editing

Split out from #65173

The UI for drag-and-drop rearrangement of apps should look like this (minus the top bar part):

<img width="200" alt="Image" src=" />

<img width="200" alt="Image" src=" />

Plus the notes from the original issue:
• The edit button on the mockup is sticky, but there is no real reason to make it so. It can just sit at the bottom of the scroll container and allocate its own space, so that it doesn't overlap with anything.
• The Cancel/Done Save buttons should be floating and sticky in case of scrolling. But if the edit button allocates its own space anyway, this should not be a concern for most cases, unless users have many apps.
• In edit mode, icons should open a menu when clicked, with options to move up/down.