HTTP API: Adds BC-layer /library/Requests.php file.

When the Requests 2.0.0 [7ef0774f0b/src/Autoload.php (L141-L143) autoloader detects the older (deprecated) `Requests` class], it attempts to load [https://github.com/WordPress/Requests/blob/v2.0.0/library/Requests.php its `/library/Requests.php` file]. Prior to this commit, this file did not exist in Core. Thus, a fatal error happened.

Why not change Requests Autoloader?
Requests is an external dependency that Core consumes. It is also used by other projects outside of Core. Thus, Core needs a fix to guard itself to prevent a fatal error.

The fix:
* Adds the missing `wp-includes/Requests/library/Requests.php` file, which then loads the `wp-includes/class-requests.php` (which will throw a deprecation notice to alert developers to upgrade).
* Adds a test.

Follow-up to [54997].

Props bjorsch, costdev, jrf, mukesh27, peterwilsoncc, ironprogrammer, hellofromTonya.
Fixes #57341.

git-svn-id: https://develop.svn.wordpress.org/trunk@55007 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/Requests/library/Requests.php

@@ -0,0 +1,12 @@
+<?php
+/**
+ * Loads the old Requests class file when the autoloader
+ * references the original PSR-0 Requests class.
+ *
+ * @deprecated 6.2.0
+ * @package WordPress
+ * @subpackage Requests
+ * @since 6.2.0
+ */
+
+include_once ABSPATH . WPINC . '/class-requests.php';

tests/phpunit/tests/http/includeOldRequestsClass.php

@@ -0,0 +1,22 @@
+<?php
+
+/**
+ * Tests that the old Requests class is included
+ * for plugins or themes that still use it.
+ *
+ * @group http
+ */
+class Tests_HTTP_IncludeOldRequestsClass extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 57341
+	 *
+	 * @coversNothing
+	 */
+	public function test_should_include_old_requests_class() {
+		$this->expectDeprecation();
+		$this->expectDeprecationMessage( 'The PSR-0 `Requests_...` class names in the Request library are deprecated.' );
+
+		new Requests();
+	}
+}