Accessibility: Make some Widgets buttons real buttons.

Links used as UI controls that behave like buttons, should be buttons.
- changes the widgets "toggle", "Delete", and "Close" links to buttons
- uses `aria-expanded` to announce the state of the toggle buttons
- increases a bit the clickable area of the toggle
- ensures the "circular focus" doesn't get cut-off in some browsers by centering the toggle arrows
- uses a `<span>` element with an `aria-hidden` attribute to hide CSS generated font icons from assistive technologies
- standardizes on `.toggle-indicator:before` rather than `:after`
- changes two `#f00` reds in `#dc3232`, see #35622

Fixes #31476.


git-svn-id: https://develop.svn.wordpress.org/trunk@40480 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/css/buttons.css

@@ -242,7 +242,7 @@ TABLE OF CONTENTS:
 
 .wp-core-ui .button-link-delete:hover,
 .wp-core-ui .button-link-delete:focus {
-	color: #f00;
+	color: #dc3232;
 }
 
 .ie8 .wp-core-ui .button-link:focus {