Allow selecting an alternative OS when rebooting
If someone has a multiboot setup and they want to boot to a different OS, it is preferable for them to select the target OS in the GNOME session, as opposed to using the Grub menu. There are two primarily reasons for this:
- The GNOME session has accessibility features and is generally more capable
- If someone is booting to Windows and Bitlocker is enabled, using the grub menu can result in them being locked out
Showing available target operating systems in the reboot dialog is probably the best solution here, since it shows the option at the point when you need it, without having to dig around elsewhere for it.
The tricky part will be correctly identifying when there are alternative operating systems that can be booted, and avoiding false positives in the list.
If we want to add this option to the reboot dialog, we'll first need to rationalise the existing content, as described in #6357.