Impossible to unhide menus after hiding them

## Use case

Hiding menus is too dangerous. Nobody remember you can unhide them with CTRL+F2 keys (in Nemo, it's ALT key, etc.). A lot of people hide them by mistake and don't know how to unhide them. Users are lost after hiding menus.

## Suggested solution

Adding a right-click menu + checkbox to unhide menus, like with Firefox.

### Possible alternatives

- Removing hiding of menus.
- Hiding menus shouldn't be so easy to do.
- Unhiding them should be done with the same mechanism than hiding them. By example, by clicking on an icon that remains after hiding menus, or something else.

No source file, test, or entry point is named. First reproduce hiding and attempting to restore menus, then locate the menu visibility handling and determine how a right-click menu or checkbox should expose the existing unhide action; done means users can reliably restore hidden menus without the keyboard shortcut.

Written by the indexing model from the issue text.