Support for `exports` in `package.json`

[sgammon]

Many packages, including react, use the exports property to define a formal module export surface.

However, GraalJs currently bails eagerly under such circumstances:

graaljs/graal-js/src/com.oracle.truffle.js/src/com/oracle/truffle/js/builtins/commonjs/NpmCompatibleESModuleLoader.java

Lines 427 to 430 in f256a80

	PackageJson pjson = readPackageJson(packageUrl, env);
	// 11.5 If pjson is not null and pjson.exports is not null or undefined, then
	if (pjson != null && pjson.hasExportsProperty()) {
	throw fail(UNSUPPORTED_PACKAGE_EXPORTS, packageSpecifier);