Cached ImmutableTrustedRedirectResponse breaks private files

Problem/Motivation

Redirect to user login in AccessDeniedSubscriber is cached for all users. This breaks viewing private files when a user without permission to view private files views a private file.

Steps to reproduce

1. Install module.
2. Submit webform with file field (file stored in private folder).
3. Anonymous user has no permission to view private files.
4. Visit private file from webform submission as anonymous user. You will be redirected to user login, this redirect is cached
5. Visit private file as authenticated user (with permission to view private files). The authenticated user is also redirected to user login, this results in a redirect loop.

Proposed resolution

Add user roles cache context to redirect response.