[8.x] Backport multiple http2 PRs
Backport of the http/2 PRs (there are several included in here... all of the http/2 related items)
Ping @addaleax
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
http2