Add forward-delete command to palette and/or mobile toolbar

This would mostly be helpful on mobile touchscreens, where there is currently only a back-delete command on soft keyboards.

Use case or problem

Moving the insertion point immediately in front of the character that needs to be deleted is often slow and fiddly on mobile touchscreens.

Proposed solution

Add a forward delete command to the command palette. It would ideal to also add a button to the stock mobile toolbar, but if necessary users can create their own with the Commander plugin once the command exists.