Fix#5776
Due to a long standing bug, faux offline message have been able to become stuck
going back years. Because of recent fixes to history loading, faux offline
messages will correctly all be sent on connection, but this causes an issue of
long stuck messages suddenly being delivered to a friend, out of context,
creating a confusing interaction. To work around this, this upgrade moves any
faux offline messages in a chat that are older than the last successfully
delivered message, indicating they were stuck, to a new table,
`broken_messages`, preventing them from ever being sent in the future.
This allows upgrade steps to query the db at the last version and run C++ code
on the results, then do a single transaction to make the upgrade, instead of
all actions of each upgrade step being required to be part of the overall
upgrade transaction.
