Refactor quic traits `Connection` and `OpenStreams` to use `self: Pin<&mut Self>` instead of `&mut self`

[Ruben2424]

The current quic traits have &mut self in the function signature. For example:

    fn poll_accept_recv(
        &mut self,
        cx: &mut task::Context<'_>,
    ) -> Poll<Result<Self::RecvStream, ConnectionErrorIncoming>>;

In the original proposal some of the trait methods had self: Pin<&mut Self> instead.
https://github.com/hyperium/h3/blob/master/docs/PROPOSAL.md#connections

It would take a large refactor to chance it now, but i think it is possible for the Connection and OpenStreams trait.

This would allow quic implementations like h3-quinn to not require Boxing the streams.

h3/h3-quinn/src/lib.rs

Lines 45 to 48 in bf078de

	incoming_bi: BoxStreamSync<'static, <AcceptBi<'static> as Future>::Output>,
	opening_bi: Option<BoxStreamSync<'static, <OpenBi<'static> as Future>::Output>>,
	incoming_uni: BoxStreamSync<'static, <AcceptUni<'static> as Future>::Output>,
	opening_uni: Option<BoxStreamSync<'static, <OpenUni<'static> as Future>::Output>>,

What do you think, is it worth the time?

With a little digging and found this comment.
#3 (comment)

This comment refes to the RecvStream trait.
The problem mentioned in the comment can be worked around for Connection and OpenStreams which only have two methods not needing Pin , which is close and opener.
Either by defining a new separate trait for close and opener or by maintaining a separate cloneable instance of OpenStreams which is not pinned.