Try loading remote image if local is not present (#23742)

Fixes #23686

Inspired by existing core functionality:
https://github.com/WordPress/wordpress-develop/blob/88c91eeaa6ab8d73bb3f5b301f9a0faf41e8e3e2/src/wp-admin/includes/image.php#L27-L37

Changes originally introduced to handle this case in:
https://core.trac.wordpress.org/changeset/20384

lib/class-wp-rest-image-editor-controller.php

@@ -147,7 +147,15 @@ public function apply_edits( $request ) {
 			return new WP_Error( 'rest_image_not_edited', $error, array( 'status' => 400 ) );
 		}
 
-		$image_editor = wp_get_image_editor( $image_file );
+		// If the file doesn't exist, attempt a URL fopen on the src link.
+		// This can occur with certain file replication plugins.
+		// Keep the original file path to get a modified name later.
+		$image_file_to_edit = $image_file;
+		if ( ! file_exists( $image_file_to_edit ) ) {
+			$image_file_to_edit = _load_image_to_edit_path( $attachment_id );
+		}
+
+		$image_editor = wp_get_image_editor( $image_file_to_edit );
 
 		if ( is_wp_error( $image_editor ) ) {
 			// This image cannot be edited.