…WP_Scripts::localize()`.

This function was previously already problematic as it does not do proper input validation, and it has already received tweaks related to PHP 8.0 in [50408] / #52534, which also introduced a `_doing_it_wrong()` notice and added tests.

The short of it is:
* The function expects to receive an `array` for the `$l10n` parameter;
* ...but silently supported the parameter being passed as a `string`;
* ...and would expect PHP to gracefully handle everything else or throw appropriate warnings/errors.

In the previous fix, a `_doing_it_wrong()` notice was added for any non-array inputs. The function would also cause a PHP native "Cannot use a scalar value as an array" warning (PHP < 8.0) or error (PHP 8.0+) for all scalar values, except `false`.

PHP 8.1 deprecated autovivification from `false` to `array`, so now `false` starts throwing an "Automatic conversion of false to array is deprecated" notice.

By rights, the function should just throw an exception when a non-array/string input is received, but that would be a backward compatibility break.

So the current change will maintain the previous behavior, but will prevent both the "Cannot use a scalar value as an array" warning/error as well as the "Automatic conversion of false to array" deprecation notice for invalid inputs.

Invalid inputs ''will'' still receive a `_doing_it_wrong()` notice, which is the reason this fix is considered acceptable.

Includes:
* Adding a test passing an empty array.
* Adding a test to the data provider for a `null` input to make sure that the function will not throw a PHP 8.1 "passing null to non-nullable" notice.

This solves the following PHP 8.1 test error:
{{{
Tests_Dependencies_Scripts::test_wp_localize_script_data_formats with data set #8 (false, '[""]')
Automatic conversion of false to array is deprecated

/var/www/src/wp-includes/class.wp-scripts.php:514
/var/www/src/wp-includes/functions.wp-scripts.php:221
/var/www/tests/phpunit/tests/dependencies/scripts.php:1447
/var/www/vendor/bin/phpunit:123
}}}

Reference: [https://www.php.net/manual/en/migration81.deprecated.php#migration81.deprecated.core.autovivification-false PHP Manual: PHP 8.1 Deprecations: Autovivification from false].

Follow-up to [7970], [18464], [18490], [19217], [50408].

Props jrf, costdev.
See #55656.

git-svn-id: https://develop.svn.wordpress.org/trunk@54142 602fd350-edb4-49c9-b593-d223f7449a82