Taxonomy: Use REST API for ajax tag search.

Deprecate wp_ajax_ajax_tag_search and switch to using the REST API when searching tags in the tags meta box.

Props nacin, chriscct7, afercia, swissspidy, jnylen0, rmccue, ryelle.
Fixes #38922.



git-svn-id: https://develop.svn.wordpress.org/trunk@42614 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/script-loader.php

@@ -726,6 +726,17 @@ function wp_default_scripts( &$scripts ) {
 				'termSelected' => __( 'Term selected.' ),
 				'termAdded'    => __( 'Term added.' ),
 				'termRemoved'  => __( 'Term removed.' ),
+				'restURL'      => rest_url( '/wp/v2/tags' ),
+
+				/**
+				 * Filters the minimum number of characters required to fire a tag search via Ajax.
+				 *
+				 * Previous to 4.8.0, this filter passed taxonomy and search context parameters.
+				 * @since 4.0.0
+				 *
+				 * @param int         $characters The minimum number of characters required. Default 2.
+				 */
+				'minChars'     => (int) apply_filters( 'term_search_min_chars', 2 ),
 			)
 		);