feature request: use default npm registry for Yarn

[zhyupe]

Currently yarn classic is downloaded from https://registry.yarnpkg.com/yarn/-/yarn-{}.tgz and yarn berry is downloaded from https://repo.yarnpkg.com/{}/packages/yarnpkg-cli/bin/yarn.js. Neither of them can make use of COREPACK_NPM_REGISTRY since it only replaces registry.npmjs.org.

Since registry.yarnpkg.com seems is only an alias of registry.npmjs.org (as they returns same bunch of ips) and there is @yarnpkg/cli-dist, maybe they could all be changed to the "default npm registry" and then works with COREPACK_NPM_REGISTRY