Export more internals so muda can be used in combination with ksni

[dfaust]

I had to expose a few internals and add some image conversion functions to make muda work with my ksni patch for the tray-icon crate.

Companion PR for tray-icon: Replace libappindicator with ksni: https://github.com/tauri-apps/tray-icon/pull/201

Tauri issue: [feat] Use ksni crate for tray icons on Linux: https://github.com/tauri-apps/tauri/issues/11293