HTTP API: Deprecate WP_Http_Curl and WP_Http_Streams classes.

These classes have not been used in WordPress Core since the Requests library was introduced in [37428]. These classes are now deprecated in favor of `WP_Http`.

There are two remaining spots in Core that reference these classes:
- The `WP_Http::_dispatch_request()` method, which was marked as deprecated in favor of `WP_Http::request()` in [42766]/[44346].
- The `WP_Http::_get_first_available_transport()`.

That latter is now also marked as deprecated in favor of `\WpOrg\Requests\Requests::get_transport_class()`.

Props SergeyBiryukov, rajinsharwar, hellofromTonya.
Fixes #58705.

git-svn-id: https://develop.svn.wordpress.org/trunk@56655 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-http.php

@@ -516,6 +516,8 @@ class WP_Http {
 	 * Tests which transports are capable of supporting the request.
 	 *
 	 * @since 3.2.0
+	 * @deprecated 6.4.0 Use WpOrg\Requests\Requests::get_transport_class()
+	 * @see WpOrg\Requests\Requests::get_transport_class()
 	 *
 	 * @param array  $args Request arguments.
 	 * @param string $url  URL to request.