Automatic merge from submit-queue (batch tested with PRs 40239, 40397, 40449, 40448, 40360)

move the discovery and dynamic clients

Moved the dynamic client, discovery client, testing/core, and testing/cache to `client-go`.  Dependencies on api groups we don't have generated clients for have dropped out, so federation, kubeadm, and imagepolicy.

@caesarxuchao @sttts 

approved based on https://github.com/kubernetes/kubernetes/issues/40363