Elevate "Editor" over "Customize" in the Appearance menu

[jameskoster]

When a block theme is active, we hide access to the Customizer in the Appearance menu. However, when certain conditions are met the link will re-appear. My concern is that it re-appears above the site editor link, which seems hierarchically inappropriate:

I suppose there are two options:

1. Adjust the priority of the Editor link, or;
2. Adjust the priority of the Customize link.

Whichever way we go, it seems sensible for the Editor link to take visual priority over the Customize link:

[Mamaduka]

I am assigning this to myself. I've PR almost ready, just need to run a few more tests :)