Request new method peer_addr for tokio::net::UdpSocket

[PragmaTwice]

Is your feature request related to a problem? Please describe.
As in the question #3309, I want to obtain peer_addr in tokio::net::UdpSocket, as std::net::UdpSocket::peer_addr.

Describe the solution you'd like
Provided by @Darksonn in Discord, implement it for mio::net::UdpSocket, then forward it to tokio::net::UdpSocket.

Describe alternatives you've considered
Provided by @Darksonn in Discord, downgrade to RawFd and retrieve peer_addr, which is a workaround.

[carlosb1]

I did a proposal , but it is necessary update mio to 0.8.0