Plugins: Tweak the plugin icons added in [41695].

- Remove plugins icons from the plugin list table, as there were performance issues loading the icons when the site had lots of plugins.
- Depending on which icons the plugin has uploaded, prefer them in this order: `svg`, `128x128`, `256x256`.
- Improve the style of the fallback icon for plugins that don't have an icon defined.

Props Travel_girl, danieltj, afercia, karmatosed,hugobaeta, empireoflight, brentjett, melchoyce, pento.
Fixes #30186.


Built from https://develop.svn.wordpress.org/trunk@41755


git-svn-id: http://core.svn.wordpress.org/trunk@41589 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/list-tables.css

@@ -1287,16 +1287,9 @@ ul.cat-checklist {
 }
 
 .wp-list-table.plugins .plugin-title,
-.wp-list-table.plugins .theme-title {
-	white-space: nowrap;
-}
-
 .wp-list-table.plugins .theme-title {
 	padding-right: 12px;
-}
-
-.wp-list-table.plugins .plugin-title {
-	padding-right: 86px; /* 64 (icon width) + 10 (icon padding) + 12 (title padding) = 86 */
+	white-space: nowrap;
 }
 
 .plugins .plugin-title img,
@@ -1308,7 +1301,11 @@ ul.cat-checklist {
 }
 
 .plugins .plugin-title .dashicons:before {
-	font-size: 64px;
+	padding: 2px;
+	background-color: #eee;
+	box-shadow: inset 0 0 10px rgba(160,165,170,.15);
+	font-size: 60px;
+	color: #B4B9BE;
 }
 
 #update-themes-table .plugin-title img,