Lazy-load comment meta on single post pages.

[34268] introduced cache priming for commentmeta, enabled by default. To
ensure performance on single post pages - where commentmeta is most likely
to cause performance issues - we disable up-front cache-priming. Instead, we
prime commentmeta caches for all comments in the loop the first time
`get_comment_meta()` is called on the page.

Props bradt, dd32, wonderboymusic, boonebgorges.
Fixes #16894.

git-svn-id: https://develop.svn.wordpress.org/trunk@34270 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment-template.php

@@ -1211,6 +1211,7 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 		'orderby' => 'comment_date_gmt',
 		'status'  => 'approve',
 		'post_id' => $post->ID,
+		'update_comment_meta_cache' => false, // We lazy-load comment meta for performance.
 	);
 
 	if ( $user_ID ) {