add @angular/core as peer dependency

[andreialecu]

The package.json does not list @angular/core as a peerDependency however it is being used in various files

This creates issues with package installers not generating a correct installation layout sometimes, especially when used with yarn workspaces.

To resolve this, @angular/core should be added to package.json/peerDependencies

Example: https://unpkg.com/@angular/material@10.2.1/package.json

[wulfsolter]

Thank you!