Buttons: Improve the .button-link CSS class for link-like buttons.

Updates `.button-link` adding color and underline to make link-like buttons look
like links by default. Introduces `.button-link-delete` as a modifier, stackable
CSS class for red button-links.

Props Cheffheid, afercia.

See #34242.
Fixes #35126.

Built from https://develop.svn.wordpress.org/trunk@40052


git-svn-id: http://core.svn.wordpress.org/trunk@39989 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/dashboard.css

@@ -771,7 +771,8 @@ form.initial-form.quickpress-open input#title {
 	min-width: 0;
 }
 
-#dashboard-widgets a {
+#dashboard-widgets a,
+#dashboard-widgets .button-link {
 	text-decoration: none;
 }