Replaces add_post_meta/update_post_meta with wpdb->insert/wpdb->update. This prevents a real-time editing session from invalidating WP_Query and various other post caches every few seconds. RTC stores awareness and sync information in post meta with high frequency. However, every call the *_post_meta functions invalidated post caches. This commit avoids this frequent invalidation by removing the direct *_post_meta calls in favor of $wpdb calls. Props czarate, mukesh27, paulkevan. Developed in https://github.com/WordPress/wordpress-develop/pull/11325. See #64696. Built from https://develop.svn.wordpress.org/trunk@62099 git-svn-id: http://core.svn.wordpress.org/trunk@61381 1a063a9b-81f0-0310-95a4-ce76da25c4cd