Move Declarative Web Request API out of experimental and make it a feature

chrome/common/extensions/api/declarative.json

 // Copyright (c) 2012 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.
 
 [
   {
-    "namespace": "experimental.declarative",
+    "namespace": "declarative",
     "internal": true,
+    "documentation_permissions_required": ["declarative"],
     "types": [
       {
         "id": "Rule",
         "type": "object",
         "description": "Description of a declarative rule for handling events.",
         "properties": {
           "id": {
             "type": "string",
             "optional": true,
             "description": "Optional identifier that allows referencing this rule."
@@ skipping 204 matching lines @@
             "type": "function",
             "parameters": [],
             "description": "Called when rules were unregistered."
           }
         ]
       }
     ]
   }
 ]