Allow $wgExtraLanguageNames override language name translations instead of only autonyms.
**Feature summary**:
```lang=php
$wgExtraLanguageNames['en']['als'] = 'Tosk Albanian';
```
```lang=php
$wgExtraLanguageNames =
'en' =>
'als' => 'Tosk Albanian';
],
];
``` in system messages or config options.
**Use case(s)**:
When we override extra language names in `$wgExtraLanguageNames` , it only allow us to override the autonyms for now.
This behavior
* Makes extra language names untranslatable (compared to when CLDR extension enabled)
* Makes language name inconsistency when overriding deprecated codes (for example, als vs. gsw)
The hook `onLanguageGetTranslatedLanguageNames` can be used for providing translated language names. However, it cannot be easily configured.
We should provide an easier way to override language name translations.