Call setFocus() when navigating

See #3661:
https://github.com/qutebrowser/qutebrowser/issues/3661#issuecomment-386308601
This doesn't seem to fully fix this, but at least the top four failed tests
there...

This should not regress #3872. Might affect #3834 in some way.

qutebrowser/browser/webengine/webenginetab.py

@@ -780,6 +780,8 @@ class WebEngineTab(browsertab.AbstractTab):
             url: The QUrl to open.
             predict: If set to False, predicted_navigation is not emitted.
         """
+        # WORKAROUND for https://bugreports.qt.io/browse/QTBUG-68076
+        self._widget.setFocus()
         self._saved_zoom = self.zoom.factor()
         self._openurl_prepare(url, predict=predict)
         self._widget.load(url)

qutebrowser/mainwindow/tabbedbrowser.py

@@ -489,6 +489,8 @@ class TabbedBrowser(QWidget):
                                                self.widget.count())
         else:
             self.widget.setCurrentWidget(tab)
+            # WORKAROUND for https://bugreports.qt.io/browse/QTBUG-68076
+            tab.setFocus()
 
         tab.show()
         self.new_tab.emit(tab, idx)