In order to optimize the use of the role cache, when the roles.yml file
is reloaded we now calculate the names of removed, changed, and added
roles so that they may be passed to any listeners. This allows a
listener to selectively clear cache for only the roles that have been
modified. The CompositeRolesStore has been adapted to do exactly that
so that we limit the need to reload roles from sources such as the
native roles stores or external role providers.

See elastic#33205