module: check file ext before dir as documented

The documented resolution algorithm started to search for package.json
files prior to searching for file extensions when searching for a
specifier. Oddly, it did not search for index files at same time it
searched for package.json. This restores the documented behavior of
searching for file extensions prior to searching directories.

PR-URL: https://github.com/nodejs/node/pull/15015
Fixes: https://github.com/nodejs/node/issues/14990


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>