fix: make sure to be able to parse big lockfiles for yarn 2

[jan-stehlik]

• [x] Tests written and linted
• [x] Documentation written / README.md updated https://snyk.io/docs/snyk-for-node/
• [x] Follows CONTRIBUTING agreement
• [x] Commit history is tidy https://git-scm.com/book/en/v2/Git-Branching-Rebasing
• [x] Reviewed by Snyk team

What this does

Support very large yarn.lock files using yarn 2 package manager.

Before:

After:

Furthermore this PR covers

• introduction of jest
• jest tests
• reorganisation of fixtures so that they can be easily accessed with both tap & jest tests
• small docs update - Readable link

Notes for the reviewer

Sorry about very big diff but most of the changes are just fixture changes, especially new huge lock file .

Most relevant files to review are:

• yarn2-lock-parser.ts
• test

To manually test please follow these steps:

npm link # in this repo
npm i && npm run build
cd snyk repo
npm link snyk-nodejs-lockfile-parser
npm run build
node dist/cli/index.js test path/to/nodejs-lockfile-parser/test/fixtures/yarn/yarn2/big

Expected result: vulnerabilies are successfully scanned

[CLAassistant]

All committers have signed the CLA.

[snyksec]

:tada: This PR is included in version 1.34.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: