Code Modernization: Use explicit visibility for class property declarations.

Using `var` or only `static` to declare a class property is PHP 4 code.

This updates the codebase to use explicit visibility modifiers introduced in PHP 5.

Props jrf.
Fixes #51557. See #22234.

git-svn-id: https://develop.svn.wordpress.org/trunk@49184 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/http/streams.php

@@ -7,5 +7,5 @@ require_once __DIR__ . '/base.php';
  * @group external-http
  */
 class Tests_HTTP_streams extends WP_HTTP_UnitTestCase {
-	var $transport = 'streams';
+	public $transport = 'streams';
 }