LibRegex+LibUnicode: Add unicode string properties

Author: https://github.com/aplefull
Commit: 7ce4abe330
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6545
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/trflynn89

Libraries/LibUnicode/CharacterTypes.h

@@ -39,6 +39,7 @@ bool code_point_has_variation_selector_property(u32 code_point);
 bool code_point_has_white_space_property(u32 code_point);
 
 bool is_ecma262_property(Property);
+bool is_ecma262_string_property(Property);
 
 Optional<Script> script_from_string(StringView);
 bool code_point_has_script(u32 code_point, Script script);