Issue #3332906: Add needed libraries to composer.json to support composer workflow

NOTE: THIS PRESERVES CDN OPTION.

In my merge request above:

• added composer.libraries.json which can be used by composer to install all external libraries,
• updates fullcalendar_view.libraries.yml to match versions and install locations of all required files,
• added Library Manager service: CDN paths processing, libraries definitions, requirements status etc.
• preserved CDN option.

Project using composer can add the following to their composer.json in order to get the libraries installed:

  // Require section:
  "require": {
    "wikimedia/composer-merge-plugin": "^2.1"
  }
  
  // Extra settings:
  "extra": {
    "merge-plugin": {
      "include": [
        "./docroot/modules/contrib/fullcalendar_view/composer.libraries.json"
      ]
    }
  }