LibCore/DateTime: Add a helper for setting the time individually

Userland/Libraries/LibCore/DateTime.cpp

@@ -90,6 +90,11 @@ void DateTime::set_time(int year, int month, int day, int hour, int minute, int
     m_second = tm.tm_sec;
 }
 
+void DateTime::set_time_only(int hour, int minute, Optional<int> second)
+{
+    set_time(year(), month(), day(), hour, minute, second.has_value() ? second.release_value() : this->second());
+}
+
 ErrorOr<String> DateTime::to_string(StringView format) const
 {
     struct tm tm;

Userland/Libraries/LibCore/DateTime.h

@@ -31,6 +31,7 @@ public:
     bool is_leap_year() const;
 
     void set_time(int year, int month = 1, int day = 1, int hour = 0, int minute = 0, int second = 0);
+    void set_time_only(int hour, int minute, Optional<int> second = {});
     ErrorOr<String> to_string(StringView format = "%Y-%m-%d %H:%M:%S"sv) const;
     ByteString to_byte_string(StringView format = "%Y-%m-%d %H:%M:%S"sv) const;