Display message being replied to above input box (#4350)

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

src/widgets/helper/MessageView.hpp

@@ -0,0 +1,50 @@
+#pragma once
+
+#include "messages/layouts/MessageLayoutContext.hpp"
+#include "messages/Message.hpp"
+#include "widgets/BaseWidget.hpp"
+
+#include <QWidget>
+
+namespace chatterino {
+
+class MessageLayout;
+
+/// MessageView is a fixed-width widget that displays a single message.
+/// For the message to be rendered, you must call setWidth.
+class MessageView : public BaseWidget
+{
+    Q_OBJECT
+
+public:
+    MessageView();
+    ~MessageView() override;
+    MessageView(const MessageView &) = delete;
+    MessageView(MessageView &&) = delete;
+    MessageView &operator=(const MessageView &) = delete;
+    MessageView &operator=(MessageView &&) = delete;
+
+    void setMessage(const MessagePtr &message);
+    void clearMessage();
+
+    void setWidth(int width);
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+    void themeChangedEvent() override;
+    void scaleChangedEvent(float newScale) override;
+
+private:
+    void createMessageLayout();
+    void layoutMessage();
+
+    MessagePtr message_;
+    std::unique_ptr<MessageLayout> messageLayout_;
+
+    MessageColors messageColors_;
+    MessagePreferences messagePreferences_;
+
+    int width_{};
+};
+
+}  // namespace chatterino