[Extensions] Enable the scripting API on stable

Bug: 1155236
Change-Id: Iea65c0fca000e16b72f176b7846b13e4c1034f89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2570074
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Auto-Submit: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833406}

chrome/common/extensions/api/_permission_features.json

@@ -748,7 +748,7 @@
     ]
   },
   "scripting": {
-    "channel": "dev",
+    "channel": "stable",
     "extension_types": ["extension"],
     "min_manifest_version": 3
   },