Add from_file_descriptors() to tty::unix

[someone13574]

Adds a function to create a Pty handle from file descriptors opened outside of Alacritty. This does not break backward compatibility.

[nixpulvis]

Is there a reason for this change? A use case for a consumer application?

[someone13574]

Is there a reason for this change? A use case for a consumer application?

I'm working on Flatpak support for Zed, which uses alacritty_terminal for it's builtin terminal, but in order to properly spawn the shell process on the host system one needs to pass the file descriptors of the command been spawned to the --forward-fd argument flatpak-spawn. This doesn't work however as alacritty doesn't expose the file descriptors until we have already passed the shell command to use, thus the need open the PTY ourselves so the fd's are available.

I figured the least intrusive way of doing this was just introducing a new function which lets you pass your own file descriptors.

[chrisduerr]

Seems simple enough and the stuff you have to do outside is also trivial (openpty).

So this solution makes more sense than basically exposing a function that is the same as openpty just with some spawn call attached.

[nixpulvis]

😄

Just letting @chrisduerr make the final review.

[chrisduerr]

Another tiny nitpick. Doubt I can find anything else.

[chrisduerr]

@someone13574 Do you need this released?

[someone13574]

@someone13574 Do you need this released?

Yes, that would be awesome.

[chrisduerr]

No promises on the ETA, but I'll try and get a release out this week.