Replace libappindicator with ksni

[dfaust]

Using ksni and the xdg standard for tray icons on Linux unlocks missing functionality and new features (#104 and more), as well as unblocks a GTK4 migration (tauri-apps/webkit2gtk-rs#94).

• Predefined menu items are not handled, except separator and about.
• Shortcuts are ignored.

Companion PR for muda:
Export more internals so muda can be used in combination with ksni: tauri-apps/muda#239

Tauri issue:
[feat] Use ksni crate for tray icons on Linux: tauri-apps/tauri#11293

[dfaust]

@amrbashir @FabianLars How do we proceed from here? The tests fail because the PR depends on tauri-apps/muda#239.

[FabianLars]

you can make tray-icon depend on the git version of muda for now

[amrbashir]

Sorry for the delay, been a bit busy IRL, and also not sure if we want to have this in tauri v2, keep old implementation and add it in tauri v2 behind a feature flag or wait for v3

[FabianLars]

if we make v3 only about switching from gtk3 to gtk4 (which imo we should) this change could wait for v3. If v3 takes ages i think it would be better to add it in v2 if that's not too much of a headache. I wouldn't put it behind a feature flag either way unless there's something missing compared to the libappindicator implementation that i don't see rn.

[dfaust]

Alright. Then please keep me updated.
And I updated the muda dependency.

[amrbashir]

I am actually leaning towards keeping the old implementation for now and adding this behind experimental feature flag (ksni) for both, tray-icon crate and tauri crate

[dfaust]

I put the ksni stuff behind a feature flag linux-ksni (I also renamed the muda feature).

I also created a new PR for tauri (tauri-apps/tauri#12319).

And it seems the compiler has become more strict. I'm still fixing the windows issues. The macos issue I don't understand, though.

[FabianLars]

the macos issue should be fixed by #220