Use Time singleton in VersionControlEditorPlugin

Instead of displaying the exact string, now Godot uses the Time
singleton to calculate the date string from the UTC Unix timestamp and
also uses Time's timezone offset conversion to string function

editor/plugins/version_control_editor_plugin.h

@@ -186,6 +186,7 @@ private:
 	void _commit_message_gui_input(const Ref<InputEvent> &p_event);
 	void _extra_option_selected(int p_index);
 	bool _is_staging_area_empty();
+	String _get_date_string_from(int64_t p_unix_timestamp, int64_t p_offset_minutes) const;
 
 	friend class EditorVCSInterface;