Linux: Use desktop portals to get dark theme information about devtoys

[badcel]

You don't need an additional DBus library as there is already a DBus implementation inside Gio which is part of Gir.Core.

You can probably just use it already as it is a dependency of Gdk, which itself is a dependency of Gtk.

I wrote a small sample to detect the color-scheme which works for me on fedora 40. Any feedback that it works on other current distributions is very welcome.

If it works, something similar should probably the base for DevToys color-scheme detection. I worked this out via the linked documentation and a tool called D-Spy.

[veler]

Hi @badcel ,

Thank you soooo much for taking the time to explain all this and to provide a sample. You made my life sooo much easier !

I made a pull request that followed your advices: #1382

Have a wonderful day !