typeahead: Tab opens typeahead if not open with a non-empty input.

Fixes part of #10026.
NOTE: The Tab key will select option from typeahead if the typeahead
is already open i.e the same behaviour as Enter.
NOTE: This behaviour applies irrespective of search pills are enabled
or not.

static/third/bootstrap/js/bootstrap.js

@@ -2026,7 +2026,7 @@
     }
 
   , move: function (e) {
-      if (!this.shown) return
+      if (!this.shown && e.keyCode != 9) return
 
       switch(e.keyCode) {
         case 9: // tab
@@ -2069,6 +2069,13 @@
           break
 
         case 9: // tab
+          if (!this.shown) {
+            this.lookup()
+            return
+          }
+          this.select(e)
+          break
+        
         case 13: // enter
           if (!this.shown) return
           this.select(e)