libei used to have direct portal support code (see the git history) but:
- that code was a custom proposed portal that never went anywhere
- libei has slowly changed to be more an input event transport layer since
it is now also used sending events *to* a libei context
- a number of libei users will never need the DBus code, either because they
don't want it or because they talk Dbus themselves na ddon't need this
abstraction.
Luckily, it's quite easy to move this into a separate library with a
simple API that does, effectively, the same trick as the old portal backend.
This API is aiming to be as simple as possible because the tools that
require anything more complex should talk to DBus directly.
An example tool that uses the API to retrieve an EIS fd over the
RemoteDesktop portal is included in this patch.
"Öffis" is a German word meaning public transport. It also sounds like the
French Œuf, the word for egg.
Co-authored-by: Olivier Fourdan <ofourdan@redhat.com>
