Draft: Add job for showing Open With dialog

Nicolas Fellarequested to merge
work/nico/openwithjob into master

Extract code from OpenUrlJob/ApplicationLauncherJob

Currently it's possible to trigger this dialog by passing a null service to ApplicationLauncherJob, but that's not intuitive.

Also add an implementation using XDG Portals to make it work in sandboxed apps

BUG: 487203

Draft because of two TODOs in the code

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