hook up can-focus to ability to tab into the widget

Change-Id: I55915254d784a0887a8d5bf6128396ab875e7ae6
Reviewed-on: https://gerrit.libreoffice.org/53634Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

starmath/uiconfig/smath/ui/catalogdialog.ui

@@ -166,7 +166,7 @@
             <child>
               <object class="GtkScrolledWindow">
                 <property name="visible">True</property>
-                <property name="can_focus">True</property>
+                <property name="can_focus">False</property>
                 <property name="hexpand">True</property>
                 <property name="vexpand">True</property>
                 <property name="hscrollbar_policy">never</property>

vcl/source/window/window2.cxx

@@ -1604,6 +1604,14 @@ bool Window::set_property(const OString &rKey, const OUString &rValue)
         if (toBool(rValue))
             GrabFocus();
     }
+    else if (rKey == "can-focus")
+    {
+        WinBits nBits = GetStyle();
+        nBits &= ~WB_TABSTOP;
+        if (toBool(rValue))
+            nBits |= WB_TABSTOP;
+        SetStyle(nBits);
+    }
     else
     {
         SAL_INFO("vcl.layout", "unhandled property: " << rKey);