Add file_load_multiple_by_uri($uri)

$ grep -R "file_load_multiple" core/ | grep uri
core/includes/file.inc:      $existing_files = file_load_multiple(array(), array('uri' => $uri));
core/includes/file.inc:      $existing_files = file_load_multiple(array(), array('uri' => $uri));
core/includes/file.inc:    $existing_files = file_load_multiple(array(), array('uri' => $file->uri));
core/includes/file.inc:      $existing_files = file_load_multiple(array(), array('uri' => $uri));
core/modules/file/file.module:  $files = file_load_multiple(array(), array('uri' => $uri));
core/modules/system/lib/Drupal/system/Tests/File/LoadTest.php:    $files = file_load_multiple(array(), array('uri' => 'foobar://misc/druplicon.png'));
core/modules/system/lib/Drupal/system/Tests/File/LoadTest.php:    $by_path_files = file_load_multiple(array(), array('uri' => $file->uri));
core/modules/image/image.module:  $files = file_load_multiple(array(), array('uri' => $uri));

All of these are being converted to entity_load_by_property() in #1184272: Remove deprecated $conditions support from entity controller, I think such a function would be really useful.