Media: Allow to omit decoding="async" on tags from wp_get_attachment_image().

When adding `decoding="async"` to images was introduced in [53480], it did not provide the ability to customize that behavior specifically for image tags returned from `wp_get_attachment_image()`.

With this changeset it is now possible to explicitly provide a `decoding` value of e.g. boolean `false` in the `$attr` parameter of the function, to ensure the attribute is omitted.

Props maximej, adamsilverstein, flixos90, costdev, peterwilsoncc, mukesh27.
Fixes #57086.


git-svn-id: https://develop.svn.wordpress.org/trunk@55171 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/media.php

@@ -1023,7 +1023,8 @@ function wp_get_attachment_image_src( $attachment_id, $size = 'thumbnail', $icon
  *                                  will result in the attribute being omitted for the image.
  *                                  Defaults to 'lazy', depending on wp_lazy_loading_enabled().
  *     @type string       $decoding The 'decoding' attribute value. Possible values are
- *                                  'async' (default), 'sync', or 'auto'.
+ *                                  'async' (default), 'sync', or 'auto'. Passing false or an empty
+ *                                  string will result in the attribute being omitted.
  * }
  * @return string HTML img element or empty string on failure.
  */
@@ -1056,6 +1057,11 @@ function wp_get_attachment_image( $attachment_id, $size = 'thumbnail', $icon = f
 
 		$attr = wp_parse_args( $attr, $default_attr );
 
+		// Omit the `decoding` attribute if the value is invalid according to the spec.
+		if ( empty( $attr['decoding'] ) || ! in_array( $attr['decoding'], array( 'async', 'sync', 'auto' ), true ) ) {
+			unset( $attr['decoding'] );
+		}
+
 		// If the default value of `lazy` for the `loading` attribute is overridden
 		// to omit the attribute for this image, ensure it is not included.
 		if ( array_key_exists( 'loading', $attr ) && ! $attr['loading'] ) {