Add a reusable admin CSS class for destructive actions

[flixos90]

As generally recommended, plugin authors should not use regular buttons for destructive actions, like removing something.

However, while there are standardized classes for buttons in WordPress admin (button, button-primary, button-secondary), a similar standardized class is missing for the destructive link. There are several locations in the admin where such links are displayed, but these are all styled using their individual selectors. Therefore plugin authors who want to use this style must either use one of these selectors (that probably do not fit the use-case at all) or recreate the style manually. Therefore I propose to standardize these style rules for a specific class, for example something like delete-button or delete-link.

[afercia]

Related: #35126.

[afercia]

Thinking at #35126 where a specific class .button-link-delete was added for this purpose, it just makes sense to me to do the same thing for links too.

[jbpaul17]

Per yesterday's bug scrub, we're going to punt this to 4.8.1.

[afercia]

Worth noting [40052] introduced .button-link-delete for <button> elements that look like links. Something similar could be done for the links.

[jbpaul17]

Per today's bug scrub, we'll punt this as the focus for 4.8.1 is regressions only.

[jbpaul17]

Punting to Future Release per today's 4.9 bug scrub.