Use package.json to manage third-party JavaScript libraries

For core development we are now using package.json and a custom build step to add third party scripts to Drupal core. This is to make it easier to stay up to date and simplify the updating process. Currently all libraries are managed this way, except CKEditor and modernizr, which requires custom builds that can't be easily automated at the moment.

To update a library

Before

1. Check each library page to see if a new version is available
2. download the latest library, from github, npm, or the library site
3. Update core and create a patch

After

Execute the following commands:

1. run yarn outdated to check what needs to be updated
2. run yarn upgrade <library> for each library that needs updating
3. run yarn vendor-update which will update the library in the core/assets/vendor folder, as well as the core.libraries.yml entry.
4. and submit the change to the core queue