More fine-grained capabilities for stories

[swissspidy]

Feature Description

This was raised by a user as a comment to 9ce45c4.

Their suggestion was to set up the capabilites for the stories editor so that they could be configured differently from posts and pages. Quote:

Create a separate user capabilities permission to differentiate with posts and pages. Easier way to imagine this is if I'm using User Role Editor plugin to change role capabilities, I would see Read Post, Read Page, Read Story and Edit Post, Edit Page, Edit Story and so on.

Personally I've used the 'Members' plugin in the past, and being able to grant users only rights to edit stories but no posts in the Members UI would be really nice.

We could probably use custom edit_story caps and the like when registering the post type, and then map_meta_cap to map to existing edit_posts cap.

Alternatives Considered

Additional Context

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Acceptance Criteria

Implementation Brief