Support Yarn 2 package manager

Yarn 2 doesn't create a node_modules folder, instead stores packages in their original archives.
https://yarnpkg.com/features/pnp#packages-are-stored-inside-zip-archives-how-can-i-access-their-files

Related: #1211

#### Docs:
https://yarnpkg.com/features/pnp#compatibility-table
https://yarnpkg.com/advanced/migration

#### Error details:

When migrating from npm to Yarn 2 (the configuration works with npm, these packages are listed in devDependencies), after `yarn install; yarn test`:
```
>> Local Npm module "grunt-eslint" not found. Is it installed?
>> Local Npm module "grunt-karma" not found. Is it installed?
>> Local Npm module "grunt-stylelint" not found. Is it installed?
>> Local Npm module "grunt-svgmin" not found. Is it installed?
```

Start by reproducing the reported `yarn install; yarn test` workflow and inspect how Grunt resolves the listed local modules: grunt-eslint, grunt-karma, grunt-stylelint, and grunt-svgmin. Use the Yarn PnP compatibility and migration links as context; done means these dependencies are recognized and the test command no longer reports them as missing.

Written by the indexing model from the issue text.