A MethodDef or a PropertyDef after linking.
Note that the version is relative to the identity of a LinkedMember.
The definition of identity varies as linked members progress through the
linking pipeline, but it only gets stronger, i.e., if two linked members
are id-different at phase P, then they must also be id-different at phase
P+1. The converse is not true. This guarantees that versions can be used
reliably to determine at phase P+1 whether a linked member coming from
phase P must be reprocessed.