Devtools: Fix tooltip z-index and add tooltip for dock side

Source/devtools/front_end/ui/tooltip.css

 /*
  * Copyright (c) 2015 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 .tooltip {
     background: hsl(0, 0%, 95%);
     border-radius: 2px;
     color: hsl(0, 0%, 20%);
     padding: 5px 8px;
     font-size: 11px;
     line-height: 14px;
     display: flex;
     align-items: center;
     -webkit-filter: drop-shadow(0 1px 2px hsla(0, 0%, 0%, 0.3));
     border: 1px solid hsla(0, 0%, 0%, 0.1);
     background-clip: padding-box;
     box-sizing: border-box;
 }
 
 .tooltip {
     position: absolute;
     visibility: hidden;
     transition: visibility 0s 100ms, opacity 150ms cubic-bezier(0, 0, .2, 1);
-    z-index: 3000;
+    z-index: 20001;
     top: 0;
     left: 0;
     opacity: 0;
 }
 
 .tooltip.shown {
     visibility: visible;
     transition-delay: 600ms;
     opacity: 1;
 }
 
 .tooltip.shown.instant {
     transition-delay: 0s;
 }
 
 .tooltip-shortcut {
     color: hsl(0, 0%, 45%);
     display: inline-block;
     margin-left: 8px;
     flex: 0 0 auto;
 }