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/singletons/WindowManager.hpp

@@ -3,6 +3,7 @@
 #include "common/Channel.hpp"
 #include "common/FlagsEnum.hpp"
 #include "common/Singleton.hpp"
+#include "common/WindowDescriptors.hpp"
 #include "pajlada/settings/settinglistener.hpp"
 #include "widgets/splits/SplitContainer.hpp"
 
@@ -25,7 +26,7 @@ public:
     WindowManager();
 
     static void encodeChannel(IndirectChannel channel, QJsonObject &obj);
-    static IndirectChannel decodeChannel(const QJsonObject &obj);
+    static IndirectChannel decodeChannel(const SplitDescriptor &descriptor);
 
     void showSettingsDialog(
         SettingsDialogPreference preference = SettingsDialogPreference());
@@ -90,6 +91,15 @@ public:
 private:
     void encodeNodeRecusively(SplitContainer::Node *node, QJsonObject &obj);
 
+    // Load window layout from the window-layout.json file
+    WindowLayout loadWindowLayoutFromFile() const;
+
+    // Apply a window layout for this window manager.
+    void applyWindowLayout(const WindowLayout &layout);
+
+    // Contains the full path to the window layout file, e.g. /home/pajlada/.local/share/Chatterino/Settings/window-layout.json
+    const QString windowLayoutFilePath;
+
     bool initialized_ = false;
 
     QPoint emotePopupPos_;