Add filter to prevent current user with an "administrator" or lms_manager" role from being changed to an "instructor"

Description

Upon closer examination of the role change process in WordPress core, it becomes evident that the default WordPress check for changing a user's role from administrator to editor fails at https://github.com/WordPress/WordPress/blob/master/wp-admin/users.php#L148. It's crucial to recognize that the correct capability name for this check is promote_users rather than edit_users. Consequently, relying on the handle_bulk_actions-users.php filter to enforce this restriction is not a viable approach. To achieve the same outcome as observed in the WordPress core, the role_has_cap filter is utilized as an alternative. Within this filter, the necessary checks and adjustments are made, ensuring that administrator and lms_manager are prevented from changing their roles to instructor.

Fixes #1100

How has this been tested?

Manually change current user role to instructor.

Screenshots

Types of changes

Checklist:

[ ] This PR requires and contains at least one changelog file.
[ ] My code has been tested.
[ ] My code passes all existing automated tests.
[ ] My code follows the LifterLMS Coding & Documentation Standards.

gocodebox / lifterlms