LibUnicode: Fully qualify use of AK::Variant in Locale.h

The generated locale data contains an enum also named Variant, as
variants are part of locale strings. This hasn't been an issue, but as
includes are reordered, the order in which the enum and AK::Variant are
included may cause an ambiguity error.

Userland/Libraries/LibUnicode/Locale.h

@@ -52,7 +52,7 @@ struct OtherExtension {
     String value {};
 };
 
-using Extension = Variant<LocaleExtension, TransformedExtension, OtherExtension>;
+using Extension = AK::Variant<LocaleExtension, TransformedExtension, OtherExtension>;
 
 struct LocaleID {
     String to_string() const;