refactor: turn StreamerMode into a singleton(-like thing) (#5216)

src/singletons/StreamerMode.hpp

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <QObject>
+
+#include <memory>
+
+namespace chatterino {
+
+class IStreamerMode : public QObject
+{
+    Q_OBJECT
+
+public:
+    IStreamerMode() = default;
+    ~IStreamerMode() override = default;
+    IStreamerMode(const IStreamerMode &) = delete;
+    IStreamerMode(IStreamerMode &&) = delete;
+    IStreamerMode &operator=(const IStreamerMode &) = delete;
+    IStreamerMode &operator=(IStreamerMode &&) = delete;
+
+    [[nodiscard]] virtual bool isEnabled() const = 0;
+
+signals:
+    void changed(bool enabled);
+};
+
+class StreamerModePrivate;
+class StreamerMode : public IStreamerMode
+{
+public:
+    StreamerMode();
+    ~StreamerMode() override;
+    StreamerMode(const StreamerMode &) = delete;
+    StreamerMode(StreamerMode &&) = delete;
+    StreamerMode &operator=(const StreamerMode &) = delete;
+    StreamerMode &operator=(StreamerMode &&) = delete;
+
+    bool isEnabled() const override;
+
+private:
+    void updated(bool enabled);
+
+    std::unique_ptr<StreamerModePrivate> private_;
+
+    friend class StreamerModePrivate;
+};
+
+}  // namespace chatterino