Import: Enhance accessibility on the Import screen.

* Remove title attributes.
* Show "Install Now" and "Details" links if the importer isn't installed yet.
* Show a "Run Importer" link if the importer is installed. It also handles activation if the plugin isn't activated.
* Add `aria-label` attributes to each link.
* Unify the importer descriptions to make them independent from the plugin state. The API was changed in [meta3690].
* Adjust JavaScript callbacks for ajaxified importer installs.

Props afercia, swissspidy, ocean90.
See #24766.
Fixes #35191.
Built from https://develop.svn.wordpress.org/trunk@38075


git-svn-id: http://core.svn.wordpress.org/trunk@38016 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/common-rtl.css

@@ -2275,15 +2275,47 @@ body.iframe {
 	display: block;
 }
 
-.importers td {
-	padding-left: 14px;
-}
-
 .importers {
 	font-size: 16px;
 	width: auto;
 }
 
+.importers td {
+	padding-left: 14px;
+	line-height: 1.5em;
+}
+
+.importers .import-system {
+	max-width: 250px;
+}
+
+.importers td.desc {
+	max-width: 500px;
+}
+
+.importer-title,
+.importer-desc,
+.importer-action {
+	display: block;
+}
+
+.importer-title {
+	color: #000;
+	font-size: 14px;
+	font-weight: 400;
+	margin-bottom: .2em;
+}
+
+.importer-action {
+	line-height: 20px; /* Same as with .updating-message */
+	color: #ddd;
+	margin-bottom: 1em;
+}
+
+.not-installed-main-site .importer-action {
+	color: #555;
+}
+
 #post-body #post-body-content #namediv h3, /* Back-compat for pre-4.4 */
 #post-body #post-body-content #namediv h2 {
 	margin-top: 0;