proposal: net: add IPConn methods to send/recv with netip.Addr

[bradfitz]

net.UDPConn has:

func (c *UDPConn) WriteToUDPAddrPort(b []byte, addr netip.AddrPort) (int, error)
func (c *UDPConn) WriteMsgUDPAddrPort(b, oob []byte, addr netip.AddrPort) (n, oobn int, err error)
func (c *UDPConn) ReadFromUDPAddrPort(b []byte) (n int, addr netip.AddrPort, err error)
func (c *UDPConn) ReadMsgUDPAddrPort(b, oob []byte) (n, oobn, flags int, addr netip.AddrPort, err error)

I propose we also add methods on IPConn, like:

func (c *IPConn) ReadFromIPAddr(b []byte) (int, netip.Addr, error)
func (c *IPConn) ReadMsgIPAddr(b, oob []byte) (n, oobn, flags int, addr netip.Addr, err error)
func (c *IPConn) WriteMsgIPAddr(b, oob []byte, addr netip.Addr) (n, oobn int, err error)
func (c *IPConn) WriteToIPAddr(b []byte, addr netip.Addr) (int, error)

/cc @andrew-d @josharian

[bradfitz]

But: the "Addr" suffix in the proposed new method names is potentially ambiguous in the same way as raised in #54234 (comment) (that is, there's a net.Addr type in addition to the netip.Addr that this is supposed to be about)