tdf#123379: implement native menu bar toggle on/off

qt5 didn't provide implementation of virtual SalMenu::ShowMenuBar
so native menu bar was visible at all times. Hopefully notebookbar
fans are happier now

Change-Id: Ie581397521369160e16f40231bade40100dcd6f6
Reviewed-on: https://gerrit.libreoffice.org/69327
Tested-by: Jenkins
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>

vcl/inc/qt5/Qt5Menu.hxx

@@ -54,6 +54,7 @@ public:
     virtual void SetSubMenu(SalMenuItem* pSalMenuItem, SalMenu* pSubMenu, unsigned nPos) override;
     virtual void SetFrame(const SalFrame* pFrame) override;
     const Qt5Frame* GetFrame() const;
+    virtual void ShowMenuBar(bool bVisible) override;
     Qt5Menu* GetTopLevel();
     virtual void SetItemBits(unsigned nPos, MenuItemBits nBits) override;
     virtual void CheckItem(unsigned nPos, bool bCheck) override;

vcl/qt5/Qt5Menu.cxx

@@ -544,6 +544,12 @@ Qt5Menu* Qt5Menu::GetTopLevel()
     return pMenu;
 }
 
+void Qt5Menu::ShowMenuBar(bool bVisible)
+{
+    if (mpQMenuBar && (bVisible != mpQMenuBar->isVisible()))
+        bVisible ? mpQMenuBar->show() : mpQMenuBar->hide();
+}
+
 const Qt5Frame* Qt5Menu::GetFrame() const
 {
     SolarMutexGuard aGuard;