RFR: 8309118: HttpClient: Add more tests for 100 ExpectContinue with HTTP/2 [v6]

[Conor Cleary]

On Tue, 24 Oct 2023 09:31:19 GMT, Conor Cleary <ccleary at openjdk.org> wrote:

>> So by checking if the final response code is received, this makes sure that the entire block of headers is processed therfore a status code will have been received.
>
> And then in the case where END_STREAM has already been seen, we call `requestBodyCF.complete(null);` to complete normally, as any RST_STREAM frames after an END_STREAM are not handled exceptionally.

I'll give these changes a go and test them, will update here when I do

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PR Review Comment: https://git.openjdk.org/jdk/pull/15664#discussion_r1369878101