This helps drive async callbacks from outside tokio-boring, such as in quiche.
Not a breaking change because every public item in tokio-boring is preserved as is.
We introduce new methods replace_ex_data for both SslContextBuilder
and Ssl in case anyone is relying on the leaking behaviour of their
set_ex_data methods, but we do document that they leak now.
These two new kinds of methods immediately return a MidHandshakeSslStream
instead of actually initiating a handshake. This greatly simplifies
loops around MidHandshakeSslStream::WouldBlock.
`tokio_boring::HandshakeError` currently requires that the inner stream
implements `Debug` for its `Display` implementation. This constraint is
unnecessary.
This change removes this `Debug` constraint so `HandshakeError` always
implements `Display`.
Anthony Ramine