Add an API to launch desktop entries

[oknozor]

Related to pop-os/launcher#119

This PR add a a method to launch desktop entries either via dbus or shell commands.

When launching an entry with the prefer_non_default_gpu option, the discrete gpu should be used either by passing the corresponding environment variables to the sub shell or via dbus.

I am not 100% confident regarding the gpu implementation since I don't have every hybrid graphics laptop available (only AMD discrete and integrated gpus), feedback would be appreciated here.

There are fake desktop entries launching glxgears -info in the ignored tests, this should be enough to test the expected gpu is used. (see https://github.com/oknozor/freedesktop-desktop-entry/blob/33f2d16b731ed80258959b2bd859fc3056d52441/src/exec/mod.rs#L252)

For the implementation to be complete we would need a launch_action method. I'll implement this after this PR has been reviewed.

[oknozor]

Just added desktop entry actions, let me know if anything needs to be changed.

[mmstick]

Seems fine, but should we also support async zbus calls?

[oknozor]

We could easily add an async api with zbus async calls and tokio::process instead of std::process. I am not sure if this would be useful though. Most of the time you just want to launch one entry and exit.

[oknozor]

@mmstick is there something more I can do ?

[mmstick]

Has this been integrated into the pop-launcher/pop-shell PR?

[jakeisnt]

Hey! Is this ready to merge yet? Would love to use it.

[jakeisnt]

@mmstick - Is this ready to go? I've been using this - it's worked well. Would love to have an official release.

[liias]

FWIW - I don't use this library for launching apps directly and would like such feature to live under a "feature" to avoid any extra dependency.

(Though I'm not sure if this repository is still maintained.)

[mmstick]

This library is maintained. It is a dependency of the COSMIC desktop.