Panel\Field::role() allow passing $roles

[distantnative]

Description

• Merge Fix $user->roles($purpose) #6653 first
• Fix User::roles() for last admin #6693
• Remove roles count check from UserPermissions #6658

Summary of changes

• Allow passing roles collection to Panel\Field::role()
• Use roles collection methods for logic instead foreach
• Only hide field if no option available. Otherwise show as radio button for transparency which role is chosen.
• User create dialog preselects first role option instead of the role of the current user (or is the assumption users create mostly other users with the same role as theirs?)

Reasoning

Different action contexts will have a different set of roles available to display. Instead of putting that logic into this UI method, it should rather allow to pass the appropriate roles collection to this helper method.

Additional context

We will modify the actual roles collection passed in the dialogs in a subsequent PR. We keep them basic for now to have no change in behavior.

Changelog

Fixes

• Panel UI fixed for create and changeRole permission and user options
  user permissions: support for options broken #5147
  user permissions: changeRole has no effect #5146

Enhancements

• Role always shown when creating a new user, even if only one role available

Ready?

• In-code documentation (wherever needed)
• Unit tests for fixed bug/feature
• Tests and CI checks all pass

[bastianallgeier]

I'm not entirely sure why, but when I test this PR in the sandbox lab, I can only add users with admin roles. The other roles vanish from the field.

[distantnative]

@bastianallgeier It's because of this https://github.com/getkirby/kirby/blob/develop-minor/src/Cms/User.php#L588-L591 - for the last admin we exit here too early. That's fine for changing the role, but not creating. Maybe we need to first merge #6657 and then can remove that check.