Add support for an IANA version in tzlookup.xml

This will enable us to require that tzlookup.xml is
touched when we pull in new IANA rules data and allow
us to detect in CTS if the overlay behavior is broken
(the code which picks up /data files in preference to
/system files).

Test: CTS: run -m CtsLibcoreTestCases
Bug: 65575839
Change-Id: I816a43fbc33e74321708a906480acd7b63aad344