Currently, when using `'type' => 'user' in an HTMLForm with 'ooui' , then autocompletion is only working for local users, not global users. This is the blocker of many tasks.
- https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/423991/
- https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/CentralAuth/+/424373/
Potential Solution
Introduce HTMLGlobalUserTextField::class in CentralAuth Extension.