Role/Capability: When checking capabilities before setting a post slug, ensure...

Role/Capability: When checking capabilities before setting a post slug, ensure the correct post type capabilities are used.

Previously, only the `publish_posts` capability was checked. Now, the correct meta or primitive capability for the post type is used where appropriate.

Props peterwilsoncc

Fixes #42464

Built from https://develop.svn.wordpress.org/trunk@42380


git-svn-id: https://core.svn.wordpress.org/trunk@42209 1a063a9b-81f0-0310-95a4-ce76da25c4cd