Introduce wp_get_user_roles() helper function

[salmanshafiq8630]

## Summary

Introduce a new helper function, wp_get_user_roles(), to provide a public API for retrieving the roles assigned to a user.

Currently, developers need to retrieve a WP_User object and access its public roles property directly:

`php
$user = get_userdata( $user_id );
$roles = $user ? $user->roles : array();
`

This requires knowledge of the internal structure of the WP_User object and exposes a public property instead of using a dedicated API.

## Proposed solution

Add a new helper function to wp-includes/user.php:

`php
/

• Retrieves the roles assigned to a user. *
• @since 7.1 *
• @param int $user_id User ID.
• @return string[] Array of role slugs. Returns an empty array if the user does not exist or has no assigned roles. */

function wp_get_user_roles( $user_id ) {

$user = get_userdata( $user_id );

if ( ! $user instanceof WP_User

empty( $user->roles ) ) {

return array();

}

return $user->roles;

}
`

## Benefits

• Provides a dedicated public API for retrieving user roles.
• Avoids direct access to the WP_User::$roles property.
• Improves readability and consistency with existing user helper functions such as wp_get_current_user().
• Simplifies a common pattern used by plugins and themes.

## Unit tests

Tests should cover:

• Valid user with a single role.
• Valid user with multiple roles.
• Invalid user ID.
• User with no assigned roles.

https://core.trac.wordpress.org/ticket/65508