Replace use of toID with ObjectIdentifier in 'ObjectIdentifier.hxx'.

Change-Id: Ic0157974eca2992167319f7d19a0224056cc985e
Reviewed-on: https://gerrit.libreoffice.org/27243Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>