Create an UploadedFile validator and deprecate error checking methods on UploadedFileInterface

Problem/Motivation

In #2940383: [PP-4] Unify file upload logic of REST and JSON:API we are wanting to upload files directly via octet-stream and Content-Disposition header, and because it doesn't use $_POST variables we can't use Symfony UploadedFile object. However, in \Drupal\file\Upload\FileUploadHandler::handleFileUpload() we call isValid() and assume we have an instance of UploadedFile.

This is most likely due to copying existing code.

Steps to reproduce

Proposed resolution

• Deprecate \Drupal\file\Upload\UploadedFileInterface::isValid()::getError() and ::getErrorMessage()
• Add an \Drupal\file\Validation\UploadedFileValidator that validates uploaded files using \Drupal\file\Validation\Constraint\UploadedFileConstraint and \Drupal\file\Validation\Constraint\UploadedFileConstraintValidator
• Remove the checks for isValid() and throwing exceptions in FileUploadHandler::handleFileUpload()
• Call UploadedFileValidator::validate() and check for constraint violations instead

Remaining tasks

Do it.

User interface changes

API changes

\Drupal\file\Upload\UploadedFileInterface::isValid()::getError() and ::getErrorMessage() are deprecated
A new UploadedFileInterface::validate() method is added, that throws \Symfony\Component\HttpFoundation\File\Exception\FileException and sub-classes.

Data model changes

Release notes snippet