Permalink edit section inherits styles brought in from add_theme_support( 'editor-styles' )

[laurelfulford]

Describe the bug
The permalink link area can inherit link styles set in a theme's classic editor styles, when they're pulled into to the new editor using add_theme_support( 'editor-styles' ).

A more specific selector, and some proactive styles should help fix, though it looks like it could be easy to end up with some redundant CSS.

This issue is similar to #11132; @afercia spotted it when reviewing changes to Twenty Seventeen, here: https://core.trac.wordpress.org/ticket/45246#comment:4

To Reproduce
Steps to reproduce the behavior:

1. Start with a theme that uses add_theme_support( 'editor-styles' ) to pull classic editor styles into Gutenberg. Any of the older default themes (Ten thru Seventeen) from the WordPress 5.0 beta will work.
2. Open an existing page or post.
3. Click on the post title to view the permalink.

Expected behavior
That this space would use the same fonts, colours, and styles of other Gutenberg elements.

Actual behavior
This space can inherit colours (on both the link and button), and font family, as well as odd things it doesn't set, like borders (Twenty Fifteen) or box-shadows (Twenty Seventeen).

Screenshots
All default themes exhibit some level of issue:

Twenty Seventeen: inherits colour and box shadow (for underline)

Twenty Sixteen: inherits colour

Twenty Fifteen: inherits colour and bottom border (for underline)

Twenty Fourteen: inherits colour on link and button

Twenty Thirteen: inherits colour on link and button

Twenty Twelve: inherits colour on link

Twenty Eleven: inherits colour, font styles

Twenty Ten: inherits colour on link and button, and font family

Additional context
Can recreate with the Gutenberg 4.2 RC, and the current version in the repo as of commit c8b4679.

[youknowriad]

We have a new panel for permalinks now #11874. We didn't remove this UI yet because we're passed UI freeze but it should be considered deprecated. I'm considering this as a wont fix.