[Quest API] Add EVENT_LEVEL_DOWN to Perl/Lua. (#2620)

* [Quest API] Add EVENT_LEVEL_DOWN to Perl/Lua.

# Perl
- Add `EVENT_LEVEL_DOWN`, exports `$levels_lost`.
- Add `$levels_gained` export to `EVENT_LEVEL_UP`.

# Lua
- Add `event_level_down`, exports `e.levels_lost`.
- Add `e.levels_gained` export to `event_level_up`.

# Notes
- Allows operators to perform actions on level down.
- Allows operators to tell how many levels were lost or gained in case people are gaining/losing multiple levels and they want to keep track or use this as a mechanic in their code somewhere.

* Update exp.cpp

* Update embparser.cpp

zone/lua_parser_events.cpp

@@ -1092,6 +1092,30 @@ void handle_player_aa_gain(
 	lua_setfield(L, -2, "aa_gained");
 }
 
+void handle_player_level_up(
+	QuestInterface *parse,
+	lua_State* L,
+	Client* client,
+	std::string data,
+	uint32 extra_data,
+	std::vector<std::any> *extra_pointers
+) {
+	lua_pushinteger(L, std::stoul(data));
+	lua_setfield(L, -2, "levels_gained");
+}
+
+void handle_player_level_down(
+	QuestInterface *parse,
+	lua_State* L,
+	Client* client,
+	std::string data,
+	uint32 extra_data,
+	std::vector<std::any> *extra_pointers
+) {
+	lua_pushinteger(L, std::stoul(data));
+	lua_setfield(L, -2, "levels_lost");
+}
+
 // Item
 void handle_item_click(
 	QuestInterface *parse,