Accessibility: Fix the `alt` attribute of the Gallery images within the Classic Editor.

Passes the images `alt` attribute value to the Gallery template used within the Classic Editor.

Props yarnboy, wpboss.
Fixes #47687.

Built from https://develop.svn.wordpress.org/trunk@45725


git-svn-id: http://core.svn.wordpress.org/trunk@45536 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/media-template.php

@@ -1361,9 +1361,9 @@ function wp_print_media_templates() {
 					<dl class="gallery-item">
 						<dt class="gallery-icon">
 							<# if ( attachment.thumbnail ) { #>
-								<img src="{{ attachment.thumbnail.url }}" width="{{ attachment.thumbnail.width }}" height="{{ attachment.thumbnail.height }}" alt="" />
+								<img src="{{ attachment.thumbnail.url }}" width="{{ attachment.thumbnail.width }}" height="{{ attachment.thumbnail.height }}" alt="{{ attachment.alt }}" />
 							<# } else { #>
-								<img src="{{ attachment.url }}" alt="" />
+								<img src="{{ attachment.url }}" alt="{{ attachment.alt }}" />
 							<# } #>
 						</dt>
 						<# if ( attachment.caption ) { #>

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45724';
+$wp_version = '5.3-alpha-45725';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.