The unit tests spend nearly half of their run time resetting the user table for
each test. But the majority of tests do not depend on the user table having the
exact value that the setup code resets it to, and do not need to modify the
user objects they require to run.
Fix that by providing an API for tests to get User objects, and to indicate
whether the User object will be subject to destructive modification or not.
This allows User objects to be reused across multiple unit tests.
Change-Id: I17ef1f519759c5e7796c259282afe730ef722e96
Anything that wants to be "central" right now has to depend on
CentralAuth, and then either can't work without CentralAuth or has to
branch all over the place based on whether CentralAuth is present. Most
of the time all it really needs is a mapping from local users to central
user IDs and back or the ability to query whether the local user is
attached on some other wiki, so let's make an interface for that in
core.
See I52aa0460 for an example implementation (CentralAuth), and Ibd192e29
for an example use (OAuth).
Bug: T111302
Change-Id: I49568358ec35fdfd0b9e53e441adabded5c7b80f
