HelpHub & Rosetta Site role conflict

[Nao]

On a Rosetta site, users can’t have HelpHub role assigned if they already have a /support/ site role.

Steps to reproduce

1. Go to ​https://ja.wordpress.org/support/wp-admin/users.php (or any other Rosetta site) and assign a user "Subscriber" role using the "Change role to..." dropdown.
2. Go to ​https://ja.wordpress.org/support/users/USERNAME screen.

This screen should show “HelpHub Role” section but it doesn’t appear if the user has a site role.
If you remove the Subscriber role, the section will show up.

Users should be able to have both HelpHub & Site roles so that HelpHub Admins of a Rosetta site can also edit things like widget and menu.

See: ​https://wordpress.slack.com/archives/CG47GT4G2/p1565919522045500

[Clorith]

4700.patch​ should, for the most part, solve this, but with one thing to take note of.

The HelpHub roles are just copying the regular post capabilities in WordPress already, so the attached patch checks if a user can edit posts, if they can't, then the management form shows up (that means for a subscriber, it will show up), but it will still be hidden for an author or editor, as they will already have access to these things already, and we do not want ot accidentally overwrite an existing role with higher access.

The patch also fixes a capability assigned to HelpHub Editors that I noticed gives the access to the customizer, this is now left purely for Managers. The reason for this access is to define the menus of the site, which are used to set up content blocks on the front page to make it simple for all to use, but a regular editor should not be making these changes.

[tellyworth]

In 9159:

HelpHub: fix role assignment for support users.

This fixes a conflict that made it impossible to set a HelpHub role for users with an existing support role.

It also removes an unnecessary edit_theme_options capability for HelpHub editors.

Props Clorith.
Fixes #4700.