Automatic merge from submit-queue (batch tested with PRs 41505, 41484, 41544, 41514, 41022)

Proxy defer on update events

This PR is a series of discrete movements in refactoring some of kube-proxy's twistier code in prep to be more async.  It should be reviewed one commit at a time.  Each commit is a smallish movement, which should be easier to examine.  I added significant tests along the way, which, unsurprisingly, found some bugs.