[welcome] Present RTL (country) annotations better

- The (RTL) text "Arabiy (Misr)" should be entirely RTL, so
   make the parenthetical insert -- which would otherwise be LTR
   and so mess up the placing of those parenthesis around the country --
   explicitly RTL.
 - Since there are no RTL languages in Calamares right now with
   country-local translations, this isn't visible.

src/modules/welcome/WelcomePage.cpp

@@ -145,7 +145,11 @@ struct LocaleLabel
         {
             sortKey.append( QString( " (%1)" )
                             .arg( QLocale::countryToString( thisLocale.country() ) ) );
-            label.append( QString( " (%1)" ).arg( thisLocale.nativeCountryName() ) );
+
+            // If the language name is RTL, make this parenthetical addition RTL as well.
+            QString countryFormat = label.isRightToLeft() ? QString( QChar( 0x202B ) ) : QString();
+            countryFormat.append( QLatin1String( " (%1)" ) );
+            label.append( countryFormat.arg( thisLocale.nativeCountryName() ) );
         }
 
         m_sortKey = sortKey;