fix(access): always display readable access level for ACCESS_* constants

Labels for global ACCESS_* constants should always be meaningful,
and not Limited. Most obvious example is when write access arrays
are not populated with ACCESS_PUBLIC in a walled garden mode.
Or else when certain global access levels are filtered by hooks
for a select group of users

Fixes #6801
chore(docs): update the docblock for get_readable_access_level()

Cleans up the warning and provides a more detailed explaination of what the function does
Merge pull request #7355 from hypeJunction/readable-acl

fix(access): always display readable access level for ACCESS_* constants