In order to factor out EntityChange as a standalone library we should remove calls that are only made from Repo

The only changes are made in:

• setRevisionInfo
• setMetadataFromRC
• setMetadataFromUser

Some random ideas for what to do:

• Create a new class inheriting from EntityChange in Repo to add the setRevisionInfo method only in Repo
• Try to remove all setter methods and instead move the logic to the Factory
• maybe we can extract the “setter” part and leave that in Lib, but move the rest of EntityChange and ClientChange to the separate package? (from https://phabricator.wikimedia.org/T257439#6315632)