Add ability to determine if permission listed in manifest.

I'm involved in the flutter_sound dart package which needs permissions for microphone and storage.

One issue we have is with users not setting up their manifest correctly.

It would be useful to be able to determine if a permission was listed in manifest (and the ios pod) so we can warn users.

Currently on android you display a message for storage:
No permissions found in manifest for: 14

Exposing the logic behind this as an api call should do the trick.
Can the same be done for ios?