http2: tidying up in core.js
A number of cleanups and improvements in core.js
Getting these out of the way before working on a larger cleanup around the lifecycle and error handling in Http2Stream and Http2Session
ping @nodejs/http2
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines
Affected core subsystem(s)
http2