caretaker note: this change does not effect G3.

Quick question: won't this break backwards compatibility with old projects that don't have ZoneJS in their dependency list, since Angular 2+ would automatically grab it?

npm (v7+) and pnpm (v7+) support auto-installing peer dependencies, including those explicitly marked as optional so that should not be a problem.

Although in general, it would be recommended to have a stricter dependency policy and avoid auto-installing peer dependency and have them explicitly listed.

This PR was merged into the repository by commit 229cdde.

The changes were merged into the following branches: main, 20.0.x

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