Provide a trait to get file upload location from field settings

Problem/Motivation

Part of #3221796: [META] Modernise file upload logic we identified that we are duplicating the code to find the file upload location in the following places:

• \Drupal\file\Plugin\Field\FieldType\FileItem::getUploadLocation()
• \Drupal\file\Plugin\rest\resource\FileUploadResource::getUploadLocation()
• \Drupal\jsonapi\Controller\TemporaryJsonapiFileFieldUploader::getUploadLocation()

We can't really create a base class and use inheritance for this, as they use different methods of uploading files (ie. UploadedFile vs input stream).

Steps to reproduce

Proposed resolution

Create a trait that gets the upload destination from the field settings, and remove the duplication.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet