Support for third party libraries in site specific and install profile specific libraries folders

In Drupal 8, contrib modules use the Libraries module to allow project to store third party libraries in different locations. There locations are:

• PATH/TO/SITE/libraries (for example sites/example.com)
• libraries
• PATH/TO/INSTALL_PROFILE/libraries

This functionality has been move to Drupal core and now libraries with locations starting with /libraries/ can be in any of these locations. They are searched in the order above and the first match found is used.

Here's an example libraries declaration:

dropzonejs:
  title: 'Dropzonejs'
  website: http://www.dropzonejs.com
  version: 4.0.1
  license:
    name: MIT
    url: https://github.com/enyo/dropzone/blob/master/LICENSE
    gpl-compatible: true
  js:
    /libraries/dropzone/dist/min/dropzone.min.js: {}
  css:
    component:
      /libraries/dropzone/dist/min/dropzone.min.css: {}

Additionally, core provides \Drupal::service('library.libraries_directory_file_finder')->find() which is the equivalent of the libraries_get_path() function.

Before

$exif_path = libraries_get_path('exif-js') . '/exif.js';

After

$library_file_finder = \Drupal::service('library.libraries_directory_file_finder')->find('exif-js/exif.js');

Modules may also use the following pattern to avoid a dependency on Drupal 8.9 and conditionally support it while also keeping optional support for the libraries module with the following pattern. This can later be simplified to just the call to the new API once the supported core version is 8.9 or higher.

if (\Drupal::hasService('library.libraries_directory_file_finder')) {
  $exif_path = \Drupal::service('library.libraries_directory_file_finder')->find('exif-js/exif.js');
}
elseif (\Drupal::moduleHandler()->moduleExists('libraries')) {
  $exif_path = libraries_get_path('exif-js') . '/exif.js';
}
else {
  $exif_path = DRUPAL_ROOT . '/libraries/exif-js/exif.js';
}