Review HTTP/2 DATA frame queueing

[sbordet]

Jetty version
10.0.0

Java version
11

Description
With the resolution of #3951, HTTP2Stream now queues DATA frames up to the flow control window size, and delivers them to listeners only if there is demand.

Before #3951, HTTP2Stream was delivering DATA frames to listeners immediately, so the queuing was happening in 2 places: either HttpInput for normal HTTP requests, or HTTP2StreamEndPoint in case of CONNECT requests.

I think we can remove the queuing from both HttpInput and HTTP2StreamEndPoint.

For HttpInput we need to consider the effects with HTTP/1.1, which I already think it overrides HttpInput in all the relevant places to not use its queuing features.

@gregw thoughts?

[gregw]

Correct, the queueing in HttpInput is only there for H2 so if it is not needed, we can probably substantially simplify HttpInput.

For h1, there is a produce API mechanism that could be adapted to take from a queue?

[sbordet]

Fixed in 10.0.0 via #4556.

[github-actions]

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