Fix spurious detection of yarn

[rotu]

Fixes #170101
Partial #193001

Previously, vscode could use find-yarn-workspace-root to identify that a package is using yarn as its package manager by looking for a package.json with the workspaces key. That is incorrect - npm and bun also use this key in their package manifest.

Now when running scripts from package.json in a multi-workspace package, it should default to npm. It should still use yarn if a yarn.lock file is detected.