Media: Generate WebP only for certain registered image sizes.

The existing filter `image_editor_output_format` receives an additional parameter `$size_name` which is populated whenever it controls the output format for a specific registered image size to create. Otherwise, it remains empty. In order to achieve this, a low level change has been added in bringing a new `$size_name` class property to the `WP_Image_Editor` base class, which is introduced in a backward compatible way that will not cause conflicts with custom implementations.

This parameter is then used in new logic inside the `wp_default_image_output_mapping()` callback function for the filter, controlling whether `image/jpeg` should map to `image/webp` output or not. By default, this is enabled for all WordPress core image sizes by default, and this list can be modified using a new `wp_image_sizes_with_additional_mime_type_support` filter, e.g. to remove core sizes or add custom sizes.

The customization per image size may be further enhanced by providing a more declarative API via a new parameter on the `add_image_size()` function.

Props eugenemanuilov, flixos90, adamsilverstein, joegrainger.

Fixes #56526.
See #55443, #56288.


git-svn-id: https://develop.svn.wordpress.org/trunk@54097 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -2690,7 +2690,7 @@ function wp_unique_filename( $dir, $filename, $unique_filename_callback = null )
 		 */
 		if ( $is_image ) {
 			/** This filter is documented in wp-includes/class-wp-image-editor.php */
-			$output_formats = apply_filters( 'image_editor_output_format', array(), $_dir . $filename, $mime_type );
+			$output_formats = apply_filters( 'image_editor_output_format', array(), $_dir . $filename, $mime_type, '' );
 			$alt_types      = array();
 
 			if ( ! empty( $output_formats[ $mime_type ] ) ) {