file_validate functions are deprecated in 10.2 and removed in 11

Problem/Motivation

We are using file_validate functions in MarkerIconService.php:

    $this->fileUploadValidators = [
      'file_validate_extensions' => !empty($this->geofieldMapSettings->get('theming.markers_extensions')) ? [$this->geofieldMapSettings->get('theming.markers_extensions')] : ['gif png jpg jpeg'],
      'file_validate_size' => !empty($this->geofieldMapSettings->get('theming.markers_filesize')) ? [Bytes::toNumber($this->geofieldMapSettings->get('theming.markers_filesize'))] : [Bytes::toNumber('250 KB')],
    ];

But these have been deprecated in 10.2, and are removed in Drupal 11 (See https://www.drupal.org/node/3363700). This module is marked as D11 compatible, so we should replace these validations with the new Contraint plugins.

Since these new constraint plugins were introduced in 10.2, and geofield_map only works on Drupal versions from 10.2 and up, we don't need to introduce any backwards compatibility. So just replacing the code is fine.