Implement hide and hidden events for tabs

Closes #14772.

js/tab.js

@@ -33,22 +33,30 @@
 
     if ($this.parent('li').hasClass('active')) return
 
-    var previous = $ul.find('.active:last a')[0]
-    var e        = $.Event('show.bs.tab', {
-      relatedTarget: previous
+    var $previous = $ul.find('.active:last a')
+    var hideEvent = $.Event('hide.bs.tab', {
+      relatedTarget: $this[0]
+    })
+    var showEvent = $.Event('show.bs.tab', {
+      relatedTarget: $previous[0]
     })
 
-    $this.trigger(e)
+    $previous.trigger(hideEvent)
+    $this.trigger(showEvent)
 
-    if (e.isDefaultPrevented()) return
+    if (showEvent.isDefaultPrevented() || hideEvent.isDefaultPrevented()) return
 
     var $target = $(selector)
 
     this.activate($this.closest('li'), $ul)
     this.activate($target, $target.parent(), function () {
+      $previous.trigger({
+        type: 'hidden.bs.tab',
+        relatedTarget: $this[0]
+      })
       $this.trigger({
         type: 'shown.bs.tab',
-        relatedTarget: previous
+        relatedTarget: $previous[0]
       })
     })
   }