Qt use platform-independent visibility functions

show() isn't just some conveniently renamed setVisible(true), but
presents a window in a platform-dependant way, which - at least
for WASM - means maximized and without a title bar. This is not
really expected and WASM can also use multiple windows.

Change-Id: I3fbaec1dfc2cd32bf3a90a94dcee01ebc88e58c7
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/128179
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

vcl/qt5/QtFrame.cxx

@@ -460,7 +460,7 @@ void QtFrame::Show(bool bVisible, bool bNoActivate)
     if (!bVisible) // hide
     {
         pSalInst->RunInMainThread([this]() {
-            asChild()->hide();
+            asChild()->setVisible(false);
             if (m_pQWidget->isModal())
                 modalReparent(false);
         });
@@ -474,7 +474,7 @@ void QtFrame::Show(bool bVisible, bool bNoActivate)
         QWidget* const pChild = asChild();
         if (m_pQWidget->isModal())
             modalReparent(true);
-        pChild->show();
+        pChild->setVisible(true);
         pChild->raise();
         if (!bNoActivate && !isPopup())
         {