LPS-49552 implement required method to use finder cache

Since LPS-47531, users of the FinderCache must supply a reference to a
BasePersistenceImpl that implements `fetchByPrimaryKeys`. For custom
finders this is never the case, so we must implement it.

An alternative implementation would inject a reference to the
appropriate persistence class and pass it to the finder cache using a
cast to BasePersistenceImpl. I've not implemented that solution as the
code would be assuming too much about the persistence
implementation (persistence impl might be overriden by a ext-plugin, so
it may not be a subclass of BasePersistenceImpl).
LPS-49552 fix other finders with the same problem