file_progress_implementation() is deprecated and replaced with extension_loaded('uploadprogress')

[github-actions]

https://www.drupal.org/node/3397577

Introduced in branch/version: 10.3.x / 10.3.0

file_progress_implementation() is deprecated and replaced with extension_loaded('uploadprogress').

As we only currently support the 'uploadprogress' extension, just checking extension_loaded('uploadprogress') simplifies this.

Before:

$implementation = file_progress_implementation()
if ($implementation === 'uploadprogress') {
  // do something
}

After:

if (extension_loaded('uploadprogress')) {
  // do something
}