Support UI language change when global preferences are present

Notable changes:
* First query global preferences to detect if global language setting
  is in use. If there is no global language setting, or if GlobalPreferences
  extension is not installed, it will fall back to changing the language
  as usual. If global language setting is found, it will add an override
  instead.
* If a local override is added, the undo tooltip is different and links to
  the global preferences page. The task design shows mw.notify style popup
  located on a bottom right corner (LTR). I deviate from the design and
  re-use the old undo tooltip with a different message instead, for
  consistency. The message is chosen depending on whether local storage
  value `uls-gp` is set to '1' (set in mw.uls.changeLanguage).
* I removed one use of deprecated mediawiki.api.options module. One other
  use still remains.
* I changed tooltip text generation from html acrobatics to use
  mw.message.parseDom. Because of that I also had to move the click handler
  to avoid buildup of click handlers.
* In message documentation fixed acronym -> autonym.

Bug: T198206
Change-Id: Ie2ed792e222be919522bd1cdea98042515a0619d

resources/js/ext.uls.common.js

@@ -50,23 +50,49 @@
 		}
 
 		deferred.done( function () {
-			var api;
+			var api = new mw.Api();
 
 			if ( mw.user.isAnon() ) {
 				changeLanguageAnon();
 				return;
 			}
 
-			api = new mw.Api();
-			api.saveOption( 'language', language )
-				.done( function () {
-					location.reload();
-				} )
-				.fail( function () {
-					// Set options failed. Maybe the user has logged off.
-					// Continue like anonymous user and set cookie.
-					changeLanguageAnon();
+			// TODO We can avoid doing this query if we know global preferences are not enabled
+			api.get( {
+				action: 'query',
+				meta: 'globalpreferences',
+				gprprop: 'preferences'
+			} ).then( function ( res ) {
+				// Check whether global preferences are in use. If they are not, `res.query` is
+				// an empty object. `res` will also contain warnings about unknown parameters.
+				try {
+					return !!res.query.globalpreferences.preferences.language;
+				} catch ( e ) {
+					return false;
+				}
+			} ).then( function ( hasGlobalPreference ) {
+				var apiModule;
+
+				if ( hasGlobalPreference ) {
+					apiModule = 'globalpreferenceoverrides';
+					mw.storage.set( 'uls-gp', '1' );
+				} else {
+					apiModule = 'options';
+					mw.storage.remove( 'uls-gp' );
+				}
+
+				return api.postWithToken( 'csrf', {
+					action: apiModule,
+					optionname: 'language',
+					optionvalue: language
 				} );
+			} ).done( function () {
+				location.reload();
+			} ).fail( function () {
+				// Setting the option failed. Maybe the user has logged off.
+				// Continue like anonymous user and set cookie.
+				changeLanguageAnon();
+			} );
 		} );
 
 		mw.hook( 'mw.uls.interface.language.change' ).fire( language, deferred );