Refactor inefficient WebSocket handshake

[benaadams]

This HandshakeHelpers class is a relic of an outdated design. Can you try simplifying this code by merging this method into the UpgradeHandshake class?

You could remove these allocations and query the header collection directly:

aspnetcore/src/Middleware/WebSockets/src/WebSocketMiddleware.cs

Lines 121 to 128 in c925f99

	var headers = new List<KeyValuePair<string, string>>();
	foreach (string headerName in HandshakeHelpers.NeededHeaders)
	{
	foreach (var value in _context.Request.Headers.GetCommaSeparatedValues(headerName))
	{
	headers.Add(new KeyValuePair<string, string>(headerName, value));
	}
	}

NeededHeaders can also be removed.

#31311 (comment)

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. Because it's not immediately obvious that this is a bug in our framework, we would like to keep this around to collect more feedback, which can later help us determine the impact of it. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[BrennanConroy]

Fixed via #31506