Provide mut access to allocated arena struct via non-cloneable ArenaBox

This commit also allows turning an `ArenaBox` into an `ArenaRef` when
non-mutable access is required, which makes `ArenaRef: Clone`. This fixes
a bug that prevented the command palette from reading all the available
actions while the `command_palette::Toggle` action was being dispatched.
73682daf38Antonio Scandurra committed on 12/21/2023, 8:41:48 AMparentca091f3
4 files changedLine totals unavailable