Alternative way to manage Yarn installation

[vojtechszocs]

Drawing inspiration from Facebook's Jest 🃏 project, there's an alternative way to manage Yarn 📦 installation.

Following steps are based on jestjs/jest#8095:

1. create .yarn/releases directory
2. copy yarn-<version>.js to .yarn/releases
3. create .yarnrc file with contents yarn-path ".yarn/releases/yarn-<version>.js"
4. exclude .yarn/* in tsconfig.json
5. git add .yarn .yarnrc tsconfig.json && git commit

The need to have some Yarn version (v1.0 or better) installed on the system remains. The yarn-path option is used to defer execution to the given binary.

As a result, both automation (e.g. 🐳 Dockerfiles) and 👨‍💼👩‍💼 developers will effectively use the same Yarn version and, even better, switching to a newer version becomes super easy.

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/cc @spadgett @jhadvig @christianvogt @priley86 @mareklibra @rawagner @jelkosz

[vojtechszocs]

Fixed by #1362 in master-next.