Storing the user name or IP in every row in large tables like revision
and logging takes up space and makes operations on these tables slower.
This patch begins the process of moving those into one "actor" table
which other tables can reference with a single integer field.
A subsequent patch will remove the old columns.
Bug: T167246
Depends-On: I9293fd6e0f958d87e52965de925046f1bb8f8a50
Change-Id: I8d825eb02c69cc66d90bd41325133fd3f99f0226
This provides a narrow view on a user identity, providing access to
ID and name.
This has been extracted from I140f43a6fb443b for re-use with Actors,
on Anomie's request.
Change-Id: Ief00db5ce382537c5bf992159eae6baf096ae4be