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

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

src/messages/MessageThread.hpp

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <QString>
+
+#include <memory>
+#include <vector>
+
+namespace chatterino {
+struct Message;
+
+class MessageThread
+{
+public:
+    MessageThread(std::shared_ptr<const Message> rootMessage);
+    ~MessageThread();
+
+    void addToThread(const std::shared_ptr<const Message> &message);
+    void addToThread(const std::weak_ptr<const Message> &message);
+
+    /// Returns the number of live reply references
+    size_t liveCount() const;
+
+    /// Returns the number of live reply references
+    size_t liveCount(const std::shared_ptr<const Message> &exclude) const;
+
+    const QString &rootId() const
+    {
+        return rootMessageId_;
+    }
+
+    const std::shared_ptr<const Message> &root() const
+    {
+        return rootMessage_;
+    }
+
+    const std::vector<std::weak_ptr<const Message>> &replies() const
+    {
+        return replies_;
+    }
+
+private:
+    const QString rootMessageId_;
+    const std::shared_ptr<const Message> rootMessage_;
+    std::vector<std::weak_ptr<const Message>> replies_;
+};
+
+}  // namespace chatterino