Check for ABSPATH exit

Is your feature request related to a problem?

To avoid direct file access, a lot of WP files disallow access if ABSPATH is not defined.
Since this essentially useful for all files that are used in the WP ecosystem, there should be a sniff for this (& perhaps even an auto-fix)

Describe the solution you'd like

if a file does not contain:

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly
}

before any other PHP code, EXCEPT if the file contains a require_once for wp-load (which would load the ABSPATH), it should give an error.

Start by reviewing the repository's existing PHP_CodeSniffer sniff structure and tests, then compare the requested ABSPATH guard and wp-load exception with current WordPress coding rules. Done means the sniff reports files missing the guard in the stated position while allowing the documented wp-load case, with coverage for the requested behavior.