NOTE: this changes the numeric values of the MIGRATION_XXX constants!
Order is preserved.
Bug: T197619
Change-Id: I16db7dd5799ab98c1cb12e7cd1e0b2da83b366fc
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