doc: sync with doxygen 1.7.6.1

The Wikimedia CI server runs doxygen 1.7.6.1, this patch sync our
configuration with that version.

TCL_SUBST and LOOKUP_CACHE_SIZE have been added.
IDL_PROPERTY_SUPPORT default value changed, unused by us though

Change-Id: Ic43d99c4675eb8f1772a72a9b9bfaf16057e19f1