LibWeb: Implement string->number for type=datetime-local input elements

Author: https://github.com/sideshowbarker
Commit: 4def3fe567
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3849
Reviewed-by: https://github.com/tcl3

Libraries/LibWeb/HTML/Dates.h

@@ -40,8 +40,21 @@ struct YearMonthDay {
     u32 day;
 };
 
+struct HourMinuteSecond {
+    i32 hour;
+    i32 minute;
+    i32 second;
+};
+
+struct DateAndTime {
+    YearMonthDay date;
+    HourMinuteSecond time;
+};
+
 Optional<YearMonthDay> parse_a_date_string(StringView);
 
+Optional<DateAndTime> parse_a_local_date_and_time_string(StringView);
+
 i32 number_of_months_since_unix_epoch(YearAndMonth);
 
 }