Spawn off a terminal emulator to install packages if needed

[davide125]

If we're not already inside a terminal, we need to run the package installation somewhere, otherwise it'll be completely invisible to the user.

[davide125]

The current implementation is a hack that just spawns off a foot terminal window. Ideally we would use the default terminal emulator of the running DE, but somewhat surprisingly there doesn't seem to be a standardized way to find out what that is... (@Conan-Kudo any ideas here?)

Long term the right solution is sorting out #1 but that's going to take a while, and we need to get this fixed before f42 ships for the FEX change.

[Conan-Kudo]

Short term, you're going to have to maintain a mapping of preferred terminals to desktops and have a fallback to foot.

Longer term, we could package up xdg-terminal-exec and get things updated so that the list is externalized and maintained properly as a global distro thing.

[davide125]

xdg-terminal-exec seems to work as-is, at least in my limited testing. Maybe we can just use that even if it's still a proposed spec? I put it up for review in https://bugzilla.redhat.com/show_bug.cgi?id=2352603

[davide125]

Switched to use xdg-terminal-exec. For now it'll fail silently if it's not installed. I plan to add some message boxes using rfd, but that needs to be packaged first, and it won't happen in time for Beta.