Improve ULS language search api

* Store prefixes and infixes separately in the data
* First match language code, then prefixes, then infixes
* Try to use suggestion either in user language or autonym first
* use formatversion=2 to avoid escaping Unicode

Using Language::fetchLanguageName might can have a small
performance impact. On the other hand there is now check
to skip languages we already found, avoiding some fuzzy
matching.

This is in a preparation for a change in jquery.uls to use
the search API more, while trying to reduce the amount of
weird autocompletion suggestions we show to the user.

Bug: T73891
Change-Id: Id94c5352d9a591969bf90144d1d2d5e758d08301

api/ApiLanguageSearch.php

@@ -22,12 +22,11 @@
  * @ingroup API
  */
 class ApiLanguageSearch extends ApiBase {
-
 	public function execute() {
 		$params = $this->extractRequestParams();
 		$search = $params['search'];
 		$typos = $params['typos'];
-		$searches = LanguageNameSearch::search( $search, $typos );
+		$searches = LanguageNameSearch::search( $search, $typos, $this->getLanguage()->getCode() );
 		$result = $this->getResult();
 		$result->addValue( null, $this->getModuleName(), $searches );
 	}