Customize: Prevent adding edit shortcuts to partial placement containers that cannot contain interactive element children

[westonruter]

In working on #38672 to allow Jetpack to extend Custom CSS to use a pre-processor, the style element in the head is turned into a selective refresh partial placement. Now with #27403 there are edit shortcut buttons that get injected into the container elements for such partial placements. In the case of a style element, however, it is illegal for it to take child elements. Not only can it cause the CSS to no longer render but also the style element is in the head and cannot be displayed anyway, so it makes no sense to inject an edit shortcut.

For more (including a workaround), see ​https://wordpress.slack.com/archives/core-customize/p1479239811000710

[westonruter]

List of elements I'm going to explicitly skip adding edit shortcuts into: area, audio, base, bdi, bdo, br, button, canvas, col, colgroup, command, datalist, embed, head, hr, html, iframe, img, input, keygen, label, link, map, math, menu, meta, noscript, object, optgroup, option, param, progress, rp, rt, ruby, script, select, source, style, svg, table, tbody, textarea, tfoot, thead, title, tr, track, video, wbr

[westonruter]

In 39270:

Customize: Prevent edit shortcut buttons from being inserted into container elements in the head or into elements which should not get interactive children.

See #27403, #38672.
Fixes #38830.