Crash was occuring because the instance info hadn't been fetched, trying
to take the last item of an empty list.
To fix:
- Expose the instance info as a state flow, with a default. New instance
info is fetched whenever the active account changes.
- Do the same for the emojis supported by the server.
- Update call sites as appropriate.
- Mark `InstanceInfoRepository` as `@Singleton` so it isn't repeatedly
created causing fresh content fetches.
The tests needed updating to get this to work.
- Extract the network fake modules in to a network-test module so
multiple other modules can use them.
- Rewrite `InstanceInfoRepositoryTest` to use Hilt and use Turbine to
test the new flows.
Checking this showed cosmetic bugs in the About layout when instance
info is missing, clean those up.
