Add webtransport-hashes to request, wired down to create a connection

[jan-ivar]

Add an associated webtransport-hashes (a webtransport-hash list) to request, and wire it down to create a connection. For use by WebTransport and CSP w3c/webappsec-csp#791.

Fixes #1880.

• At least two implementers are interested (and none opposed):
  • Chrome, Firefox, Safari
• Tests are written and can be reviewed and commented upon at:
  • PR aims to be behavior neutral with existing tests in https://wpt.fyi/results/webtransport
• Implementation bugs are filed: none revealed as of yet from this change
• MDN issue is filed: None planned (aims to be behavior neutral)
• The top of this comment includes a clear commit message to use.

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Preview | Diff

[jan-ivar]

Build appears to have stalled on infra unrelated to PR? ("Run pip install bikeshed && bikeshed update") cc @annevk

[annevk]

I rebased (which should address the CI issue you encountered) and pushed a commit addressing a number of nits. This looks good to me, but I have a couple of questions that might result in a couple more tweaks.

Note that I had to force push to your branch so you'll have to reset if you want to commit and push again.

[jan-ivar]

@annevk Thanks for your help! If we merge this one first, then w3c/webappsec-csp#791 and w3c/webtransport#711 can follow.