http2: fix respondWithFile and respondWithFD headers_sent.
When using respondWithFile or respondWithFD the headersSent flags was never set to true. Fix it to set state.flags to STREAM_FLAGS_HEADERS_SENT after processing headers into these methods.
Fixes: https://github.com/nodejs/node/issues/18862
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines