Coding Standards: Move wp-includes/class-http.php to wp-includes/class-wp-http.php.
This renames the file containing the WP_Http class to conform to the coding standards.
This commit also includes:
- A new
class-http.php that includes the new file, for anyone that may've been including the file directly.
- Replaces references to the old filename with the new filename.
Follow-up to [8516], [13274], [33748].
Fixes #54389. See #53359.