Site Health: Update the icon used when no issues are reported.

The icon used to be a rather blocky checkmark, but has now been changed to the more friendly, and less ambiguous, smiley dashicon.

It also helps cover a rare cases where a checkmark, while often used to mark something as done, may also be used to indicate that something is incorrect (many thanks to my 6th grade teacher for this rationale).

As an added bonus, this commit also adjusts the margins used around the icon, to make it fit more nicely on both large and small viewports.

Props sabernhardt, generosus.
Fixes #53980.

git-svn-id: https://develop.svn.wordpress.org/trunk@52018 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/site-health.css

@@ -249,12 +249,12 @@ are styled in the Privacy section of edit.css */
 	text-align: center;
 	height: 100%;
 	width: 100%;
-	margin-top: 0;
+	margin: 0 0 3rem;
 }
 
 @media all and (min-width: 784px) {
 	.site-status-all-clear {
-		margin: 5rem 0;
+		margin: 2rem 0 5rem;
 	}
 }
 
@@ -264,7 +264,8 @@ are styled in the Privacy section of edit.css */
 
 .site-status-all-clear .dashicons {
 	font-size: 150px;
-	height: 130px;
+	height: 150px;
+	margin-bottom: 2rem;
 	width: 150px;
 }
 

src/wp-admin/site-health.php

@@ -200,7 +200,7 @@
 <div class="health-check-body health-check-status-tab hide-if-no-js">
 	<div class="site-status-all-clear hide">
 		<p class="icon">
-			<span class="dashicons dashicons-yes"></span>
+			<span class="dashicons dashicons-smiley" aria-hidden="true"></span>
 		</p>
 
 		<p class="encouragement">