tdf#109304: Seems infobar child window wasn't registered in Math

thus no signature status infobar appeared (I wonder if read-only
bar ever worked too)

Change-Id: I8829b2b6a17fb8d38e3ea79b87d544e3fb29f1c1
Reviewed-on: https://gerrit.libreoffice.org/40377Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>
(cherry picked from commit a542fe8d)
Reviewed-on: https://gerrit.libreoffice.org/40387

starmath/source/view.cxx

@@ -36,6 +36,7 @@
 #include <sfx2/docfilt.hxx>
 #include <sfx2/docinsert.hxx>
 #include <sfx2/filedlghelper.hxx>
+#include <sfx2/infobar.hxx>
 #include <sfx2/msg.hxx>
 #include <sfx2/objface.hxx>
 #include <sfx2/printer.hxx>
@@ -879,6 +880,7 @@ void SmViewShell::InitInterface_Impl()
 
     GetStaticInterface()->RegisterChildWindow(SmCmdBoxWrapper::GetChildWindowId());
     GetStaticInterface()->RegisterChildWindow(SmElementsDockingWindowWrapper::GetChildWindowId());
+    GetStaticInterface()->RegisterChildWindow(SfxInfoBarContainerChild::GetChildWindowId());
 }
 
 SFX_IMPL_NAMED_VIEWFACTORY(SmViewShell, "Default")