Merge branch 'dropdown-persits-filtered-data' into 'master'

Fixed issue with filtered data persisting when dropdown closed

![labels](/uploads/4b9c902add76263d8488cc34ef49f142/labels.gif)

Closes #14401

See merge request !3302

app/assets/javascripts/gl_dropdown.js.coffee

@@ -167,7 +167,11 @@ class GitLabDropdown
 
   hidden: =>
     if @options.filterable
-      @dropdown.find(".dropdown-input-field").blur().val("")
+      @dropdown
+        .find(".dropdown-input-field")
+        .blur()
+        .val("")
+        .trigger("keyup")
 
     if @dropdown.find(".dropdown-toggle-page").length
       $('.dropdown-menu', @dropdown).removeClass PAGE_TWO_CLASS