Added support for Twitch's Chat Replies (#3722)

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

src/widgets/dialogs/ReplyThreadPopup.hpp

@@ -0,0 +1,48 @@
+#pragma once
+
+#include "ForwardDecl.hpp"
+#include "widgets/DraggablePopup.hpp"
+
+#include <boost/signals2.hpp>
+#include <pajlada/signals/scoped-connection.hpp>
+#include <pajlada/signals/signal.hpp>
+
+namespace chatterino {
+
+class MessageThread;
+class Split;
+class SplitInput;
+
+class ReplyThreadPopup final : public DraggablePopup
+{
+    Q_OBJECT
+
+public:
+    ReplyThreadPopup(bool closeAutomatically, QWidget *parent, Split *split);
+
+    void setThread(std::shared_ptr<MessageThread> thread);
+    void giveFocus(Qt::FocusReason reason);
+
+protected:
+    void focusInEvent(QFocusEvent *event) override;
+
+private:
+    void addMessagesFromThread();
+    void updateInputUI();
+
+    // The message reply thread
+    std::shared_ptr<MessageThread> thread_;
+    // The channel that the reply thread is in
+    ChannelPtr channel_;
+    Split *split_;
+
+    struct {
+        ChannelView *threadView = nullptr;
+        SplitInput *replyInput = nullptr;
+    } ui_;
+
+    std::unique_ptr<pajlada::Signals::ScopedConnection> messageConnection_;
+    std::vector<boost::signals2::scoped_connection> bSignals_;
+};
+
+}  // namespace chatterino