copy IsolationSelection package over from 21.2

This is pretty much a 1-to-1 copy of the packages as is in 21.2 (plus two enums in xAODPrimitives), followed by replacing the use of TAccept with AcceptData+AcceptInfo.

For the MR shifter: Since this is a copy from another branch, it should get a "review lite", i.e. please only comment on actual problems, and refrain from making stylistic comments, etc.