refactor: Make Args less of a singleton (#5041)

This means it's no longer a singleton, and its lifetime is bound to our application.
This felt like a good small experiment to see how its changes would look
if we did this.
As a shortcut, `getApp` that is already a mega singleton keeps a
reference to Args, this means places that are a bit more difficult to
inject into call `getApp()->getArgs()` just like other things are
accessed.

src/widgets/FramelessEmbedWindow.cpp

@@ -64,13 +64,13 @@ bool FramelessEmbedWindow::nativeEvent(const QByteArray &eventType,
 
 void FramelessEmbedWindow::showEvent(QShowEvent *)
 {
-    if (!getArgs().parentWindowId)
+    if (!getApp()->getArgs().parentWindowId)
     {
         return;
     }
 
     if (auto parentHwnd =
-            reinterpret_cast<HWND>(getArgs().parentWindowId.value()))
+            reinterpret_cast<HWND>(getApp()->getArgs().parentWindowId.value()))
     {
         auto handle = reinterpret_cast<HWND>(this->winId());
         if (!::SetParent(handle, parentHwnd))