Confusing preview behavior

## Describe the bug

I'm attempting to use `previewPermissionStatuses` to customize previews for different scenarios but it looks like `PreviewMultiplePermissionsState` doesn't actually adapt to a change in permissions.

A quick look at [the code](https://github.com/google/accompanist/blob/fda7f06a24a42b0b1afa75591e768d82d2941984/permissions/src/main/java/com/google/accompanist/permissions/MultiplePermissionsState.kt#L122-L127) suggests that only `PreviewPermissionsState.permissions` is an accurate reflection making properties like `shouldShowRationale` and code to detect partial permissions like the following unavailable:

```kotlin
locationPermissionsState.permissions.size == locationPermissionsState.revokedPermissions.size
```

It appears that in a preview `shouldShowRationale` always returns `false` and the partial permission code above will always be `true` because the revoked permissions list is always empty.