feat(node-resolve): add native node es modules support (rollup#413)

Ref rollup#412

Enable native node es modules via "exports" field in package.json.
Added custom plugin to generate nested package.json with {"type": "module"}
as an alternative to mjs extension usage. This works similar to rollup distribution.
https://unpkg.com/browse/rollup@2.10.9/dist/es/

packages/node-resolve/package.json

@@ -10,7 +10,7 @@
   "author": "Rich Harris <richard.a.harris@gmail.com>",
   "homepage": "https://github.com/rollup/plugins/tree/master/packages/node-resolve/#readme",
   "bugs": "https://github.com/rollup/plugins/issues",
-  "main": "dist/index.js",
+  "main": "./dist/cjs/index.js",
   "engines": {
     "node": ">= 8.0.0"
   },
@@ -75,6 +75,11 @@
       "!**/types.ts"
     ]
   },
-  "module": "dist/index.es.js",
+  "exports": {
+    "require": "./dist/cjs/index.js",
+    "import": "./dist/es/index.js"
+  },
+  "module": "./dist/es/index.js",
+  "type": "commonjs",
   "types": "types/index.d.ts"
 }

packages/node-resolve/rollup.config.js

@@ -1,6 +1,8 @@
 import babel from 'rollup-plugin-babel';
 import json from '@rollup/plugin-json';
 
+import { emitModulePackageFile } from '../../shared/rollup.config';
+
 import pkg from './package.json';
 
 export default {
@@ -22,7 +24,7 @@ export default {
   ],
   external: Object.keys(pkg.dependencies).concat(['fs', 'path', 'os', 'util']),
   output: [
-    { file: pkg.main, format: 'cjs' },
-    { file: pkg.module, format: 'es' }
+    { file: pkg.main, format: 'cjs', exports: 'named' },
+    { file: pkg.module, format: 'es', plugins: [emitModulePackageFile()] }
   ]
 };