This is more consistent with LoadBalancer, modern, and inclusive
of master/master mysql, NDB cluster, and MariaDB galera cluster.
The old constant is an alias now.
Change-Id: I0b37299ecb439cc446ffbe8c341365d1eef45849
MediaWiki:Foo.json and User:Foo/bar.json pages now have a default
content model of JSON, but existing pages using those names will be set
to defaults of wikitext.
The content models of those pages are now set to "json", unless it has
invalid syntax, in which case it will be set to "wikitext".
For convenience, the script is automatically run as part of update.php.
Bug: T108663
Change-Id: I1412937ccea8e65dba58580beec79cbf2286ae01
