Improve information displayed in a network's sites list table

* Better support for arbitrary domain/path combinations by displaying the URL in the primary column rather than Path or Domain.
* Show a cached count of total users per site as a more useful data point rather than the first 5 users.
* Clear that cached count of users for a site when a user is added to the site via `add_user_to_blog()`.

Props @ocean90.
Fixes #32434.


git-svn-id: https://develop.svn.wordpress.org/trunk@32718 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/list-tables.css

@@ -259,7 +259,7 @@ table.fixed {
 }
 
 .fixed .column-posts {
-    width: 74px;
+	width: 74px;
 }
 
 .fixed .column-comment .comment-author {
@@ -1510,6 +1510,15 @@ div.action-links,
 	background: #fecac2;
 }
 
+.sites.fixed .column-lastupdated,
+.sites.fixed .column-registered {
+	width: 20%;
+}
+
+.sites.fixed .column-users {
+	width: 80px;
+}
+
 /* =Media Queries
 -------------------------------------------------------------- */