JMH Benchmarks and optimised ActorPath parser (for Validation)

This ports the new actor path parser from PR: https://github.com/akka/akka/pull/16352 to master and
brings back JMH benchmarks to master (issue https://github.com/akka/akka/issues/16372) as well (so that the ActorPath PR can include it's benchmarks).

The field which we had to keep as deprecated in ActorPath (the regex) in 2.3 is removed from this commit - we do not need to keep it for binary compat on 2.4.x

refs #16344
refs #16372