handshake: use new crypto/tls 0-RTT API (#4953)

* handshake: simplify method signature of cryptoSetup.handleEvent

* use the new crypto/tls 0-RTT API

internal/handshake/fake_conn.go

@@ -0,0 +1,21 @@
+package handshake
+
+import (
+	"net"
+	"time"
+)
+
+type conn struct {
+	localAddr, remoteAddr net.Addr
+}
+
+var _ net.Conn = &conn{}
+
+func (c *conn) Read([]byte) (int, error)         { return 0, nil }
+func (c *conn) Write([]byte) (int, error)        { return 0, nil }
+func (c *conn) Close() error                     { return nil }
+func (c *conn) RemoteAddr() net.Addr             { return c.remoteAddr }
+func (c *conn) LocalAddr() net.Addr              { return c.localAddr }
+func (c *conn) SetReadDeadline(time.Time) error  { return nil }
+func (c *conn) SetWriteDeadline(time.Time) error { return nil }
+func (c *conn) SetDeadline(time.Time) error      { return nil }