Improve capabilities management when registering custom taxonomy

[slaFFik]

Currently we have such caps when using register_taxonomy() ​codex:

'manage_terms' - 'manage_categories'
'edit_terms' - 'manage_categories'
'delete_terms' - 'manage_categories'
'assign_terms' - 'edit_posts'

IMO, setting manage_terms to false block access to page (cheating message),
setting edit_terms to false displays this message: "You are not allowed to edit this item.", which is very odd. Editing means editing, So I should not be able to use Quick Edit and Edit links (they should be hidden).

Also, I propose to add a create_terms capability maping - for displaying the add term form and giving ability to create them, separately from editing/deleting.

Related: #22511

[danielbachhuber]

+1 to a pass on improving capabilities for managing terms, and offering flexibility on par with register_post_type()

[danielbachhuber]

Related #22511

[johnjamesjacoby]

Related #35614

[Biranit]

I am very much in a need for create_terms capability for taxonomies. Is this something that is currently being considered?