Added x-attach-split-to-window command line arg (#2411)

Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/widgets/FramelessEmbedWindow.hpp

@@ -0,0 +1,25 @@
+#pragma once
+
+#include "widgets/BaseWindow.hpp"
+
+namespace chatterino {
+
+class Split;
+
+class FramelessEmbedWindow : public BaseWindow
+{
+public:
+    FramelessEmbedWindow();
+
+protected:
+#ifdef USEWINSDK
+    bool nativeEvent(const QByteArray &eventType, void *message,
+                     long *result) override;
+    void showEvent(QShowEvent *event) override;
+#endif
+
+private:
+    Split *split_{};
+};
+
+}  // namespace chatterino