Rename http3Only to requireUnreliable

[annevk]

This should be more future proof.

Fixes #1744.

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[jasnell]

Given this work-in-progress "Quic for Streams" draft https://www.ietf.org/archive/id/draft-kazuho-quic-quic-on-streams-00.html ... which would allow implementing a functional subset of QUIC on top of TLS, I'm not sure "requireUnreliable" makes sense

[annevk]

@jasnell presumably a WebTransport user that sets requireUnreliable to true would not want such a connection though? Maybe it does mean we should explicitly say HTTP/3 over UDP when we give examples?

[ronag]

What does requireUnreliable even mean in a practical sense? Why would I ever want to require that something is "unreliable"? It just sounds weird... enableUnreliable, allowUnreliable etc. maybe is less confusing?

[annevk]

That's the term https://w3c.github.io/webtransport/ uses as public API and it's for them, so might as well stick with it. What it means is described in this PR.

[ekinnear]

Thank you! This seems like it strikes a good balance between describing the needs at a high level and being clear and precise enough for implementation at a lower level.

[annevk]

Thanks! I've pushed mt's suggestion. I will merge this on Monday barring any other comments.

[annevk]

Thanks, given there's been feedback that resulted in further changes I will merge it this week Thursday now to give everyone a chance to look again.