Themes: Move the skip link to outside the canvas in block themes

Fix Twenty Twenty-one having an erroneous margin above the Header template part
by moving the skip link outside of the wp-site-blocks canvas.

This is a backport of https://github.com/WordPress/gutenberg/pull/34986.

Props youknowriad.
Fixes #54491.




Built from https://develop.svn.wordpress.org/trunk@52243


git-svn-id: http://core.svn.wordpress.org/trunk@51835 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/theme-templates.php

@@ -165,7 +165,7 @@ function the_block_template_skip_link() {
 	<script>
 	( function() {
 		var skipLinkTarget = document.querySelector( 'main' ),
-			parentEl,
+			sibling,
 			skipLinkTargetID,
 			skipLink;
 
@@ -176,10 +176,10 @@ function the_block_template_skip_link() {
 
 		// Get the site wrapper.
 		// The skip-link will be injected in the beginning of it.
-		parentEl = document.querySelector( '.wp-site-blocks' );
+		sibling = document.querySelector( '.wp-site-blocks' );
 
 		// Early exit if the root element was not found.
-		if ( ! parentEl ) {
+		if ( ! sibling ) {
 			return;
 		}
 
@@ -197,7 +197,7 @@ function the_block_template_skip_link() {
 		skipLink.innerHTML = '<?php esc_html_e( 'Skip to content' ); ?>';
 
 		// Inject the skip link.
-		parentEl.insertAdjacentElement( 'afterbegin', skipLink );
+		sibling.parentElement.insertBefore( skipLink, sibling );
 	}() );
 	</script>
 	<?php

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52242';
+$wp_version = '5.9-alpha-52243';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.