file_validate functions are deprecated, removed in D11

Problem/Motivation

Per this change record: https://www.drupal.org/node/3363700 → file validate functions are deprecated in 10.2 and removed in Drupal 11. This prevents new section templates from being created with images.

Steps to reproduce

In a Drupal 11 site, attempt to add a new template with an image.

Proposed resolution

Replace the deprecated functions with the new format.