doc: correct esm spec package scope lookup definition
This corrects the logic in the READ_PACKAGE_SCOPE
method where it was returning the parsed package.json contents instead of the URL followed by a second read phase. In the process READ_PACKAGE_SCOPE
has been renamed to LOOKUP_PACKAGE_SCOPE
to more clearly reflect the definition of this return value.
Fixes: https://github.com/nodejs/node/issues/40578
@nodejs/modules