Add direct access check to /wp-includes/blocks/index.php

[peterwilsoncc]

Related to #60352.

As servers are typically set to use index.php as a default when directories are accessed, the use of the file in /wp-includes/blocks/ can result in filling the logs files with noise due to fatal errors as search engines test the URL for validity.

As a temporary fix for this, I suggest adding an ABSPATH check to the file and dying gracefully to prevent noise.

There is a ​pull request linked to the earlier ticket that can be used as a starting point.

https://core.trac.wordpress.org/ticket/62108

[mukesh27]

#62121 was marked as a duplicate.

As mention in ticket description there is already a PR ​https://github.com/WordPress/wordpress-develop/pull/6635

[peterwilsoncc]

In 59117:

Editor: Prevent direct access to /wp-includes/blocks/index.php.

Adds a check for ABSPATH to the top of the /wp-includes/blocks/index.php file and prevents the file from loading if it is not defined.

This prevents the file from throwing errors when accessed directly.

Props khokansardar, mukesh27.
Fixes #62108.
See #60352.