Add support for `package.json` `exports` field

[sgammon]

If a module package.json specifies exports, GraalJs will now read them and prefer exports over standard resolution; export types can be registered by the developer as preferred. In lieu of these types (and as a default), the following export types are preferred, in order:

• graaljs
• import (in ESM)
• require
• default

Fixes and closes oracle/graaljs#903

This is quick and dirty and probably not mergeable as expressed, but we are using it effectively downstream.

cc / @woess

[sgammon]

I don't know how to add tests to GraalJs yet. I'm happy to figure it out and add tests if there is any desire to merge this

[woess]

Happy to accept contributions in that area. The commonjs support has been a bit neglected tbh...

We will need some test coverage for it.

I think you can find most of the tests here: graal-js/src/com.oracle.truffle.js.test/src/com/oracle/truffle/js/test/builtins/CommonJSRequireTest.java graal-js/src/com.oracle.truffle.js.test/commonjs graal-js/src/com.oracle.truffle.js.test/src/com/oracle/truffle/js/test/builtins/CommonJSWithCustomFsTest.java

[sgammon]

@woess Thanks for the review. I'll take a look at adding some tests

[0c3d7r4]

This is great, especially Conditional exports support. Could also support patterns

  "exports": {
    "./features/*.js": "./src/features/*.js"
  },

for

import featureX from 'es-module-package/features/x.js';