History sharing: resume key-bundle import on restart (#5214)
* Store rooms pending key bundles in the CryptoStore
Replace the in-memory storage of which rooms are waiting for a key bundle with
permanent storage in the crypto store.
* Clear pending-key-bundle flag on malformed bundles
If we cannot import the key bundle, there is no point trying again another
time: we may as well clear the flag either way.
* Factor out some helpers in history sharing integ test
* Do not accept key bundles for rooms we joined more than 24h ago
Per discussion in crypto-internal.
* Clear pending key bundle data when we leave a room
* Resume key-bundle import on restart
* Clear pending-key-bundle flag on rooms that we joined ages ago
* fixup! Clear pending-key-bundle flag on malformed bundles