Config import allows invalid role import

Problem/Motivation

When i add a non-existent permission to a role yml, the config is imported without error. However this can lead to a broken user experience because the permission form cannot then be save.

Steps to reproduce

* Edit user.role.authenticated.yml and add a made-up permission "foobar".
* Import the role through the config import "single item" UI, copying the yaml with the foobar permission
* (Note the role imports successfully)
* Go to the permissions page, and save it.

Adding non-existent permissions to a role is not allowed. The incorrect permissions are "foobar"

Proposed resolution

I assume that the config import form should be subjected to the same validation checks. It may also be that the user permission form should simply warn off the removed permissions?

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet