net: Add take_error to TcpSocket and TcpStream

[mxinden]

Motivation

When manually creating a TcpSocket or TcpStream e.g. via tokio::net::TcpStream::try_from one should be able to check for errors after awaiting the connection to be writable (writable()) before assuming the connection to be successfully established.

This is needed e.g. in rust-libp2p, see libp2p/rust-libp2p#2458.

Solution

The first commit reintroduces #4364 which first merged but later on reverted in #4392. See also #4392 (comment).

The second commit adds the same method to TcpStream.

Tagging @taiki-e as the initial author.

[Darksonn]

Thanks!

[mxinden]

Thanks a lot, both for the quick merge and for the general maintenance! 🙏