Merge citra-emu PR#3159 by FearlessTobi(citra-qt : Fix a bug in our fullscreen implementation)

src/yuzu/main.h

@@ -128,6 +128,8 @@ private slots:
     void OnToggleFilterBar();
     void OnDisplayTitleBars(bool);
     void ToggleFullscreen();
+    void ShowFullscreen();
+    void HideFullscreen();
     void ToggleWindowMode();
     void OnCoreError(Core::System::ResultStatus, std::string);