Defer cookie block checks to resolve a circular dependency

Defer cookie block checks to resolve a circular dependency

User needs to load user preferences to get preferred language, which
calls User::load() which calls User::loadFromSession().

User::loadFromSession() tries to load blocks which might use messages
which need user language which calls User::load() because the previous
call to it haven't completed yet...

We have a protection against infinite recursion to prevent this from
completely crashing MW, however this patch fixes the main issue: loading
too much stuff when a User is initialized.

Bug: T180050
Change-Id: I63af6d2239b36124d5ed382b8d2aab82c8d54d69