client/tailscale/apitype: move local API types to new apitype package

They were scattered/duplicated in misc places before.

It can't be in the client package itself for circular dep reasons.

This new package is basically tailcfg but for localhost
communications, instead of to control.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tailcfg/tailcfg.go

@@ -1050,12 +1050,6 @@ func eqTimePtr(a, b *time.Time) bool {
 	return ((a == nil) == (b == nil)) && (a == nil || a.Equal(*b))
 }
 
-// WhoIsResponse is the JSON type returned by tailscaled debug server's /whois?ip=$IP handler.
-type WhoIsResponse struct {
-	Node        *Node
-	UserProfile *UserProfile
-}
-
 // Oauth2Token is a copy of golang.org/x/oauth2.Token, to avoid the
 // go.mod dependency on App Engine and grpc, which was causing problems.
 // All we actually needed was this struct on the client side.