Custom Jest resolver with node exports package entry points support

This package aims to bring node exports package entry points support to Jest, i.e.:
``javascript
// some.test.js
import { Foo } from 'my-package/submodule';
import { Bar } from '@my-scope/package/submodule';
// ...
`

This is heavily discussed in the following issue #9771.
Several alternatives proposed, such as
using enhanced-resolve,
writing own resolver based on firebase-jest-testing resolver,
using custom resolver written for esfx.

This package is a slightly generalized version of the firebase-jest-testing self-resolver:
- test import path for referencing submodule (including @scoped/ packages);
- try to load that package's package.json;
- check for exports field, try to find 'node', 'require' or 'default' (in case of type !== 'module') condition;
- reuse defaultResolver with updated target.

$3

Install:
`shell
yarn add jest-node-exports-resolver -D
`

Add custom resolver jest config option:
`javascript
// jest.config.js
module.exports = {
// ...
resolver: 'jest-node-exports-resolver',
}

``

$3

Node.js supports two flavours of 'exports':
- conditions list: when all the entries contain keywords ('import', 'require', 'node' etc.);
- entry points list: when all the entries contain submodule paths ('.', './submodule-a', './submodule-b/*' etc.).

Only the latter one is supported. Feel free to send a PR with conditions list support.