tools: only fetch previous versions when necessary

Refactor the logic for working out the previous versions of Node.js for
the API documentation so that the parsing (including the potential https
get) happens at most once per build (as opposed to the current once per
generated API doc).

Signed-off-by: Richard Lau <riclau@uk.ibm.com>

PR-URL: https://github.com/nodejs/node/pull/32518
Fixes: https://github.com/nodejs/node/issues/32512


Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>