With this patch deprecation warnings will be emitted
if $wgUser is accessed or written into. The only pattern
of usage still allowed is
$oldUser = $wgUser;
$wgUser = $newUser;
// Do something
$wgUser = $oldUser;
Once there is no deprecation warnings, we know that nothing
legitimately depends on $wgUser being set, so we can safely
remove the code that's still allowed as well.
Bug: T267861
Change-Id: Ia1c42b3a32acd0e2bb9b0e93f1dc3c82640dcb22
