Debugger: move implementation to a separate folder.

src/debug/debug.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 "use strict";
 
 // Default number of frames to include in the response to backtrace request.
 var kDefaultBacktraceLength = 10;
 
 var Debug = {};
 
@@ skipping 2549 matching lines @@
     case 'string':
     case 'number':
       json = value;
       break;
 
     default:
       json = null;
   }
   return json;
 }