Currently when searching for a remote to provide the runtime for an app,
we search remotes in priority order. This commit makes it so we search
the remote providing the app before others with the same priority, and
otherwise still search in priority order. This means for the common
case where every remote has the default priority of 1, the app's origin
will have the first chance to provide the runtime. This behavior seems
logical, but the impetus for this change was also to keep a unit test
passing in eos-updater[1] after a port to FlatpakTransaction.
Originally the eos-updater unit test was written to prioritize the
origin remote regardless of the priorities on any other remote, but
during code review it was decided to let higher priority remotes stay
above the app's origin.
In practice it's usually true that only one remote provides a runtime
and priorities aren't set at all, so this is an edge case that probably
doesn't come up much.
A unit test and documentation updates are included.
[1] eede0a8b9c/tests/test-update-install-flatpaks.c (L1919)
845a877ce1