Handle mul wikisource pages

[Parthiv-M]

Modify Wikidata query to include
mul wikisource and handle it in
related methods as well

Bug: T345325

[samwilson]

With this, WikisourceApi::fetchWikisources() returns a lot of duplicates for mul, e.g. the output of examples/list.php includes the following:

* pa - ਪੰਜਾਬੀ - Q28861316
* ml - മലയാളം - Q22004659
* li - Limburgs - Q24577674
* mul - لغات متعددة - Q18198097
* mul - distintes llingües - Q18198097
* mul - çoxdilli - Q18198097
* mul - бер нисә тел - Q18198097
* mul - некалькі моў - Q18198097
* mul - некалькі моваў - Q18198097

It's slightly odd, because this library never really thought about Multilingual Wikisource to start with (sorry! that's my fault), and so it has a language code and name for each Wikisource (e.g. Wikisource::$langName). For Multilingual Wikisource these should probably return mul and a localised name, perhaps from multiple languages (Q20923490). That's not particularly satisfactory, but do you think it'll make sense enough? Either that, or we could explicitly separate mulwikisource from the others, so consuming code would have to change.

[Parthiv-M]

Ah, I did see this in the output, but was not sure what to make of it.

I'm not entirely sure I get what you mean by localised name. Does that mean we don't need to show the names некалькі моў, некалькі моваў, etc.?

How would the output be formatted then?