...as the trivial derivations (used to offer "convenience ctors") didn't
override Clone(), so -fsanitize=vptr would cause warnings like

> sd/source/ui/dlg/layeroptionsdlg.cxx:42:26: runtime error: downcast of address 0x603001dff830 which does not point to an object of type 'const SdAttrLayerName'
> 0x603001dff830: note: object is of type 'SfxStringItem'
>  61 05 80 1e  70 d6 f7 22 67 7f 00 00  01 00 00 00 4e 6e 00 be  60 f8 df 01 30 60 00 00  02 00 00 00
>               ^~~~~~~~~~~~~~~~~~~~~~~
>               vptr for 'SfxStringItem'
>     #0 0x7f66931db4b0 in SdInsertLayerDlg::SdInsertLayerDlg(vcl::Window*, SfxItemSet const&, bool, rtl::OUString const&) sd/source/ui/dlg/layeroptionsdlg.cxx:42:26

when doing "Insert - Layer..." in Draw.

Change-Id: I54ade09027daecc8bbf6f4789a8b5318bbe8d22d