tools: update JSON header parsing for backticks

Methods, events, and so on in headers in our documentation may (and
should) be set off with backticks in the raw markdown. When that
happens, the headers is misinterpreted by tools/json.js as not being a
method or event. Update the JSON tool generator to accommodate backticks
in this situation and add a test for this situation.

Fixes: https://github.com/nodejs/node/issues/31290

PR-URL: https://github.com/nodejs/node/pull/31294


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>