The old notation <lang>-<ruleset> is not supported anymore. It is
now interpreted as a ruleset reference without a ruleset and just
referencing a single rule. Also the release number notation is
not supported anymore.
Since RuleSetReferenceId is Internal+Deprecated, no API changes.
Clarified External/Internal: A RuleSetReference is either absolute
(RuleSet is known) or relative (RuleSet is not known).
Fixes#4313
7b24edc0db