esm: Implement esm mode flag

This provides a mode: "esm" flag for package.json files which will treat ".js" files as ES modules within a given package boundary.

The package boundary of a package.json file is deemed to be all modules in that folder and subfolder until the next nested package.json file.

The plan is to add a top-level --mode flag to this, roughly matching the npm proposal, but restricted to the current package boundary. This work is currently at https://github.com/guybedford/node/tree/package-top-mode.

The mode effectively marks a directory as an "esm mode" directory, where all ".js" files in that directory are loaded as ES modules, unless they are located in a subfolder that contains a package.json without an "esm mode", which results in reverting to the transparent interop of treating ".js" as CommonJS.

In addition this PR enables caching of package.json lookups within the ES module resolver.

Presentation: https://docs.google.com/presentation/d/1xK1ana_TIxfAHX33CYVHFnJsV0If_YirLtRBBga9cv0/edit#slide=id.p

This work is based on the following prior proposal work:

• package.json "esm" flag (nodejs/node-eps/pull/60), where this replaces the PR from https://github.com/nodejs/node/pull/18156
• npm's --mode proposal (https://gist.github.com/ceejbot/b49f8789b2ab6b09548ccb72813a1054#parse-goals)
• package mime goals (https://gist.github.com/bmeck/7ee7eb2147e2dafe3167c856d9b4151a)

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

esmodules