Remove Unnecessary Includes in Headers (#4275)

* refactor: remove unnecessary includes in headers

* fix: formatting

* chore: changelog

* fix: scrollbar

* fix: suggestions and old appbase remains

* fix: suggestion

* fix: missing Qt forward declarations

* fix: another qt include

* fix: includes for precompiled-headers=off

* Add missing `<memory>` includes

* Add missing `#pragma once`

* Fix tests

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/providers/irc/Irc2.hpp

@@ -1,8 +1,6 @@
 #pragma once
 
 #include "common/SignalVector.hpp"
-#include "providers/irc/IrcChannel2.hpp"
-#include "providers/irc/IrcServer.hpp"
 
 #include <rapidjson/rapidjson.h>
 
@@ -10,6 +8,10 @@ class QAbstractTableModel;
 
 namespace chatterino {
 
+class Channel;
+using ChannelPtr = std::shared_ptr<Channel>;
+class IrcServer;
+
 enum class IrcAuthType { Anonymous, Custom, Pass, Sasl };
 
 struct IrcServerData {