Exceptions classes are nearly always value objects, and should in most
cases by newable.
Bug: T247862
Change-Id: I4faa8ec6ea8bc44086cfc8075b32d10eea61e9df
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
