The a-c side of this work is in https://github.com/mozilla-mobile/android-components/pull/6128
This switches Fenix to use `SyncableLoginsStorage`, which caches a connection internally
on first access, and doesn't expose any lock/unlock APIs at the public boundary.
This removes Fretboard. The goal is to reduce cold startup costs associated with loading the experiments on the main thread. We currently have two experiments frameworks in use and should only require one.
Grisha Kruglov