LibUnicode: Move Unicode-aware case transformations to a helper file

These will be needed by AK::String as well, so move them to a helper
file where they can be re-used.

Meta/Lagom/Tools/CodeGenerators/LibUnicode/GenerateUnicodeData.cpp

@@ -781,6 +781,8 @@ struct CodePointDecomposition {
 
 Optional<Locale> locale_from_string(StringView locale);
 
+Span<SpecialCasing const* const> special_case_mapping(u32 code_point);
+
 }
 )~~~");