SplitContainer refactor (#4261)

* Remove unused include util/Helpers.hpp

* SplitContainer::setTag fix parameter naming

* autofy/constify where possible

* More const auto ptr magicifying

* Make SplitNode::Type an enum class

* Move QuickSwitcherPopup includes from header to source file

* Remove unused DropRegion code

* use empty() instead of size() == 0

* Add curly braces everywhere

* Remove useless reinterpret_cast

It was casting Node* to Node*

* Clarify that the connect is QObject::connect

* SplitContainer::setSelected fix parameter naming

* Rename function variables to remove unneccesary underscore

Also move addSpacing parameter out of the layout function

* emplace_back where possible

* Name parameters

* Remove ineffective const from return type

* Make node getters const

* Flatten Node::releaseSplit

* Rename in-function variable to match code style

* [ACTUAL CODE CHANGE/MOVE] Move clamp logic to its own function

* name params

* applyFromDescriptorRecursively: rename node param to baseNode

* [ACTUAL CODE CHANGE/MOVE] Remove the many overloads for append/insertSplit

This utilizes the C++20 designed initializers aggregate initialization feature

* Remove unused includes

* [ACTUAL CODE CHANGE] Clean up dragging logic

There's no need to keep a pointer around to which split is being
dragged, it's already stored in the QDropEvent source()

* UNRELATED .clang-tidy: Only suggest UPPER_CASE for constant global variables

* Remove unused SplitContainer::getSplitCount function

* Use std::max in Node's clamp function

* Remove test code

* DraggedSplit.hpp: remove unused include

* Split `setDraggingSplit` into two functions, `startDraggingSplit` and `stopDraggingSplit`

src/widgets/dialogs/switcher/QuickSwitcherPopup.cpp

@@ -1,6 +1,7 @@
 #include "widgets/dialogs/switcher/QuickSwitcherPopup.hpp"
 
 #include "Application.hpp"
+#include "common/Channel.hpp"
 #include "singletons/Theme.hpp"
 #include "singletons/WindowManager.hpp"
 #include "util/LayoutCreator.hpp"
@@ -10,6 +11,8 @@
 #include "widgets/helper/NotebookTab.hpp"
 #include "widgets/listview/GenericListView.hpp"
 #include "widgets/Notebook.hpp"
+#include "widgets/splits/Split.hpp"
+#include "widgets/splits/SplitContainer.hpp"
 #include "widgets/Window.hpp"
 
 namespace chatterino {