[IMPR] derive ParamInfo from collections.abc.Sized
[IMPR] derive ParamInfo from collections.abc.Sized

- ParamInfo is a sized container. Derive this class from
  collections.abc.Sized too and make __len__ definition
  mandatory

Change-Id: I1e38db40818ba8c03f1b125e08e36cce4d1dd4cf

wikimedia/pywikibot-core,wikimedia/pywikibot-core