Split up Window Layout loading into a loading and application stage (#1964)

* Split up Window Layout loading into a loading and application stage

Previously, we were creating UI elements at while we were reading the window-layout.json file.
We now read the window-layout.json file fully first, which results in a
WindowLayout struct which is built up of a list of windows with a list
of tabs with a root node which contains containers and splits.
This WindowLayout can then be applied.

This will enable PRs like #1940 to start Chatterino with Window Layouts
that aren't defined in a json file.

This commit has deprecated loading of v1 window layouts (we're now on v2). If a v1 window layout is there, it will just be ignored and Chatterino will boot up as if it did not have a window layout at all, and on save that old window layout will be gone.

* Fix compile error for mac

src/widgets/splits/SplitContainer.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "common/WindowDescriptors.hpp"
 #include "widgets/BaseWidget.hpp"
 
 #include <QDragEnterEvent>
@@ -184,8 +185,6 @@ public:
     void selectNextSplit(Direction direction);
     void setSelected(Split *selected_);
 
-    void decodeFromJson(QJsonObject &obj);
-
     int getSplitCount();
     const std::vector<Split *> getSplits() const;
 
@@ -201,6 +200,8 @@ public:
     static bool isDraggingSplit;
     static Split *draggingSplit;
 
+    void applyFromDescriptor(const NodeDescriptor &rootNode);
+
 protected:
     void paintEvent(QPaintEvent *event) override;
 
@@ -214,6 +215,9 @@ protected:
     void resizeEvent(QResizeEvent *event) override;
 
 private:
+    void applyFromDescriptorRecursively(const NodeDescriptor &rootNode,
+                                        Node *node);
+
     void layout();
     void selectSplitRecursive(Node *node, Direction direction);
     void focusSplitRecursive(Node *node);
@@ -221,7 +225,6 @@ private:
 
     void addSplit(Split *split);
 
-    void decodeNodeRecusively(QJsonObject &obj, Node *node);
     Split *getTopRightSplit(Node &node);
 
     void refreshTabTitle();