8370024: HttpClient: QUIC congestion controller doesn't implement pacing

[djelinski]

Implement pacing for QUIC.

This is required by RFC 9002. Also, it improves the network utilization on links with long round-trip times.

The pacing algorithm itself was created based on the suggestions found in RFC 9002, and on the description of the Linux pacing algorithm.

Pacing is enabled when the round-trip time is less than twice the period at which the selector timeout fires. On Linux the selector timeout fires every millisecond, on Windows it's 15.6 milliseconds by default.

HttpClient tests came back clean.

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Issue

• JDK-8370024: HttpClient: QUIC congestion controller doesn't implement pacing (Bug - P3)

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• 00: Full (dab80e58)