Media: Output WebP by default when uploading JPEGs.

Uploaded JPEGs will automatically be converted to WebP sub-sizes instead of JPEG, saving space and making sites faster.

The original JPEG upload is always retained and can be accessed by calling `wp_get_original_image_url`.

Props azaozz, flixos90.
Fixes #55443.



git-svn-id: https://develop.svn.wordpress.org/trunk@54086 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/media.php

@@ -3843,3 +3843,18 @@ function wp_media_attach_action( $parent_id, $action = 'attach' ) {
 		exit;
 	}
 }
+
+/**
+ * Filters the default image output mapping.
+ *
+ * With this filter callback, WebP image files will be generated for certain JPEG source files.
+ *
+ * @since 6.1.0
+ *
+ * @param array $output_mapping Map of mime type to output format.
+ * @retun array The adjusted default output mapping.
+ */
+function wp_default_image_output_mapping( $output_mapping ) {
+	$output_mapping['image/jpeg'] = 'image/webp';
+	return $output_mapping;
+}