Add browser and module field support to package.json processing

[anmonteiro]

This PR fixes #2433 by introducing a new option, packageJsonEntryNames, which allows specifying a list of ordered entries which the compiler should look for when resolving Node modules. The default is the single entry "main".

When compiling for the web, however, we would pass in a list of "browser", "main" which tells the compiler to look for a "browser" entry before checking the "main" entry.

This also allows people who want to consume packages that instead rely on es2015:main or esnext:main to include those too in the order of precedence they prefer.

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[anmonteiro]

I signed it!

[googlebot]

CLAs look good, thanks!

[ChadKillingsworth]

The PR itself looks good - a flag can be added later for CLI usage.

@anmonteiro Do you have any idea how prevalent the browser field advanced usage form is? https://github.com/defunctzombie/package-browser-field-spec#replace-specific-files---advanced

That's been my largest hangup on this to date.

[Deraen]

Just three example that were present in dependency tree of react, react-dom, leaflet, react-leaflet:
https://github.com/nodejs/readable-stream/blob/master/package.json#L41
https://github.com/ashtuchkin/iconv-lite/blob/master/package.json#L40
https://github.com/kriskowal/asap/blob/master/package.json#L16

[anmonteiro]

Interesting. I didn't know about the advanced usage of the browser field.

I have no idea how prevalent it is, but my intuition would be to solve that as needed.

This PR introduces basic support for it, and we can build on it later.

[ChadKillingsworth]

@dimvar LGTM. We'll continue to iterate on this in future PRs.

[dimvar]

OK, I'll import and submit the PR internally.