doc: use code markup/markdown in headers
This also allows us to remove backslash escaping for [
and ]
inside of header code, which makes the bare markdown more readable.
Refs: https://github.com/nodejs/node/pull/31086
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