bug#41342: Add context menu when right-clicking tab in tab-bar-mode

[Juri Linkov]

> Please consider adding a context menu to tab-bar-mode shown when
> clicking a tab.  This could including actions such as:
>
> - Close tab
> - Close other tabs
> - Duplicate tab

These are added now.

> Inspired by Firefox, one could also imagine.
>
> - Move tab
>   - Move to Start (of list)
>   - Move to End
>   - Move to New Frame

This would be easy to add but I'm not sure if they are needed
because it's easier to drag tabs to move them,
and indeed Chromium has no such menu items.