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>

CHANGELOG.md

@@ -24,7 +24,7 @@
 - Dev: Ignore `WM_SHOWWINDOW` hide events, causing fewer attempted rescales. (#4198)
 - Dev: Migrated to C++ 20 (#4252, #4257)
 - Dev: Enable LTO for main branch builds. (#4258, #4260)
-- Dev: Removed unused include directives. (#4266)
+- Dev: Removed unused include directives. (#4266, #4275)
 - Dev: Removed TooltipPreviewImage. (#4268)
 - Dev: Removed unused operators in `Image` (#4267)