[DX] Add user_role_has_permission function

Description of the need

A module may want to do something conditional on whether a role has a permission. Other functions can be used in a roundabout way, but this would be simpler.

Proposed solution

A simple function called user_role_has_permission that takes a role name and a permission name and returns a boolean if the role has the permission.

Alternatives that have been considered

For now, I've added this code in my module.

Is there a Drupal or Backdrop contributed module that accomplishes this? no

Additional information

Add any other information or screenshots that would help.

Draft of feature description for Press Release (1 paragraph at most)

Backdrop now includes an additional function for modules to check whether a user role includes a permission.

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PR added at https://github.com/backdrop/backdrop/pull/4486