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/common/SignalVectorModel.hpp

@@ -10,6 +10,12 @@
 
 namespace chatterino {
 
+template <typename T>
+class SignalVector;
+
+template <typename T>
+struct SignalVectorItemEvent;
+
 template <typename TVectorItem>
 class SignalVectorModel : public QAbstractTableModel,
                           pajlada::Signals::SignalHolder