Review sniff handling of PHP 7.4 null coalesce equal operator

[dingo-d]

Since PHP 7.4 null coalesce equal operator was introduced (??=).

Now instead of using null coalesce operator when assigning to a variable like:

$_GET['variable'] = $_GET['variable'] ?? 'default';

You can write

$_GET['variable'] ??= ''default';

We need to see what sniffs cover usage of this operator upstream and in the utils and if we can just use them in the WPCS ruleset.

Refs:

• PHP RFC: https://wiki.php.net/rfc/null_coalesce_equal_operator

Related to #764