Replace service ID strings with class constants in the file module

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Problem/Motivation

Outside its tests, the file module fetches 42 services by string ID. Every one of those services has a class or interface alias. #3049525: Enable service autowiring by adding interface aliases to core service definitions added the aliases for core services and #3325557: Enable more service autowiring by adding interface aliases to core modules added them for module services. Since #3490713: Return the correct typehint when Drupal::service() is called with a class string, \Drupal::service() returns the correct type when you pass it a class name. With a string ID, IDEs can't follow the reference and PHPStan can't check the type.

Steps to reproduce

Proposed resolution

Change the string IDs to the alias class constants in these places:

• \Drupal::service() calls in File, ComputedFileUrl, FileFieldItemList, FileItem, FileWidget, FileAccessControlHandler, ManagedFile, FormFileUploader and FileUsageBase.
• $container->get() calls in the create() methods of FileVideoFormatter, FileUploadResource and five constraint validators.

For example, \Drupal::service('file.usage') becomes \Drupal::service(FileUsageInterface::class).

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet