This adds the basic infrastructure for the Permissions API, including
the `Permissions` and `PermissionStatus` interfaces. The API is exposed
via `navigator.permissions` on both `Window` and `WorkerGlobalScope`.
- `is_permission_supported` is hardcoded to return false.
- The `query()` method checks for a secure context but rejects all
queries since no powerful features are supported yet.
The permission store and permission key related methods and algorithms.
Ability for the user agent to store the permissions entries.
Passes a few more subtests in `permissions/`.
https://wpt.live/permissions/idlharness.any.htmlhttps://wpt.live/permissions/idlharness.any.worker.htmlhttps://wpt.live/permissions/edge-cases.https.html
This one behaves differently because now the `query` property is
defined. And the last subtest passes for the wrong reason.
"Querying "fullscreen" permission with "allowWithoutGesture" false
is unsupported"
but in fact everything is currently unsupported.
https://wpt.live/fullscreen/api/permission.tentative.https.html
permission is marked as experimental in Navigator and WorkerNavigator,
so tests that now pass actually don't because the tests don't have
access to the interfaces.
