Nav Menus: Use WP_Query for quick searches.

`the_post()` sets the `$in_the_loop` property to true which is unexpected in the admin if you're using filters which should only affect real loops.

Props ruud@joyo.
Fixes #27042.

git-svn-id: https://develop.svn.wordpress.org/trunk@37881 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/menu/wpAjaxMenuQuickSearch.php

@@ -0,0 +1,29 @@
+<?php
+
+/**
+ * @group menu
+ */
+class Tests_Menu_WpAjaxMenuQuickSeach extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 27042
+	 */
+	public function test_search_returns_results_for_pages() {
+		include_once ABSPATH . 'wp-admin/includes/nav-menu.php';
+
+		self::factory()->post->create_many( 3, array( 'post_type' => 'page', 'post_content' => 'foo' ) );
+		self::factory()->post->create( array( 'post_type' => 'page', 'post_content' => 'bar' ) );
+
+		$request = array(
+			'type'            => 'quick-search-posttype-page',
+			'q'               => 'foo',
+			'response-format' => 'json',
+		);
+
+		$output = get_echo( '_wp_ajax_menu_quick_search', array( $request ) );
+		$this->assertNotEmpty( $output );
+
+		$results = explode( "\n", trim( $output ) );
+		$this->assertCount( 3, $results );
+	}
+}