Docs: Replace "Current theme" with "Active theme" in various DocBlocks.

This change replaces "Current theme" with "Active theme" in various DocBlocks for better consistency with user-facing strings.

Follow-up to [52580].

Props Presskopp, audrasjb, costdev.
Fixes #54831.
See #54770.

Built from https://develop.svn.wordpress.org/trunk@52610


git-svn-id: http://core.svn.wordpress.org/trunk@52198 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/update.php

@@ -568,7 +568,7 @@ function wp_update_themes( $extra_stats = array() ) {
 	$checked = array();
 	$request = array();
 
-	// Put slug of current theme into request.
+	// Put slug of active theme into request.
 	$request['active'] = get_option( 'stylesheet' );
 
 	foreach ( $installed_themes as $theme ) {