libservo: Flesh out permissions API (#35396)

- Update the script crate to better reflect the modern Permission
  specifcation -- removing the necessity for an `Insecure` variant of
  the permissions prompt.
- Have all allow/deny type requests in the internal API use an
  `AllowOrDeny` enum for clarity.
- Expose `PermissionsRequest` and `PermissionFeature` data types to the
  API and use them in the delegate method.
- Update both servoshell implementations to use the API.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Mukilan Thiyagarajan <mukilan@igalia.com>

components/script_bindings/codegen/Bindings.conf

@@ -596,7 +596,10 @@ Dictionaries = {
 
 Enums = {
 'GPUFeatureName': {
-    'derives': ['Hash', 'Eq']
+    'derives': ['Eq', 'Hash', ]
+},
+'PermissionName': {
+    'derives': ['Eq', 'Hash']
 }
 }