LibUnicode: Do not limit language display names to known locales

Currently, the UnicodeLocale generator collects a list of known locales
from the CLDR before processing language display names. For each locale,
the identifier is broken into language, script, and region subtags, and
we create a list of seen languages. When processing display names, we
skip languages we hadn't seen in that first step.

This is insufficient for language display names like "en-GB", which do
not have an locale entry in the CLDR, and thus are skipped. So instead,
create the list of known languages by actually reading through the list
of languages which have a display name.

Userland/Libraries/LibUnicode/Forward.h

@@ -25,7 +25,7 @@ enum class GeneralCategory : u8;
 enum class HourCycle : u8;
 enum class HourCycleRegion : u8;
 enum class Key : u8;
-enum class Language : u8;
+enum class Language : u16;
 enum class ListPatternStyle : u8;
 enum class ListPatternType : u8;
 enum class Locale : u16;