add a context to OpenStream and NewStream

[marten-seemann]

Fixes #86, using option 1.

Associated PRs (These PRs will all need to be rebased after we've merged this PR and cut a new release):

• use a context for OpenStream and NewStream go-libp2p-swarm#232
• use a context when opening streams go-libp2p#1033
• add the context to NewStream() in the mock conn implementation go-libp2p-kad-dht#701
• pass contexts to OpenStream in tests go-libp2p-transport-upgrader#70
• pass contexts to OpenStream in tests go-libp2p-testing#31
• pass a context to OpenStream in tests go-ws-transport#98
• change OpenStream to accept a context go-libp2p-quic-transport#189
• change OpenStream to accept a context go-libp2p-yamux#29
• change OpenStream to accept a context go-libp2p-mplex#21
• change OpenStream to accept a context go-libp2p-webrtc-direct#35

[marten-seemann]

CI is failing because this is a breaking API change. Obviously it is...

[Stebalien]

LGTM once we have all the related PRs in place.

[Stebalien]

All the transport PRs LGTM as well. @raulk can we get a final signoff on the change? This should have minimal to no impact on downstream users (unless they explicitly try to create a new stream on a specific connection, but most users just call host.NewStream(...).

[raulk]

@marten-seemann could you please announce the upcoming change in discuss.libp2p.io?

[marten-seemann]

@marten-seemann could you please announce the upcoming change in discuss.libp2p.io?

Should we do that when we actually cut a release of go-libp2p?

Status of the merge:
All PRs merged, expect for libp2p/go-libp2p-webrtc-direct#35 (build is broken, repo doesn't seem to be maintained) and libp2p/go-libp2p-kad-dht#701 (depends on go-libp2p).
We might want to make sure that go-yamux and go-mplex respect the context before actually cutting a new release of go-libp2p (with the current changes, they just conform to the new interface but ignore the context). Still waiting for PRs to get reviewed on the respected repos.