Customize: Publish settings section overlaps controls pane on larger monitors

[westonruter]

As reported in #39896 by @bduclos :

CSS bug: for large screens, the new publish panel is overlapped by the controls panel. Inside customize-controls.css, the following lines are missing:

@media screen and (min-width: 1667px){
    .outer-section-open .wp-full-overlay.expanded {
        margin-left: 18%;
    }
}

For more specifics on what needs to be done, see [40511] for how the width of the controls pane was made variable for #32296..

[sayedwp]

WIP PR ​https://github.com/xwp/wordpress-develop/pull/268

[sayedwp]

I am also fixing other minor UI issues in this PR.

[westonruter]

In 41677:

Customize: Fix positioning of outer section (e.g. publish settings) on large screen sizes.

Also fix preview link CSS for desktop and mobile.

Props sayedwp, bduclos.
See #39896.
Fixes #42051.