MediaItem Resolver

Nobody has claimed this yet.

## 🚀 Feature Requests

This is really importend request for my app.
I have a youtube manager app, I would like to have an `url` resolver or `MediaItem` resolver.
### Describe the feature
Ok say that i have a list of `MediaItem`,
with diffrrent URLs
`https://www.youtube.com/watch?v=ZulwKDO-6B4&list=FLNp78z85NAdOtLgH16l-T7Q&index=27`

`XamarinMediaManager` should point to a `MediaItem` resolver, before starting to play the mediaItem.
The resolver could then change URI/ decrypt it so the library could then play it.

This Feature should be a global one in the library.
I dont know of this kind of Feature is available right now as i have checked.
### Why this is importend
Think if you have a list of videos, 20 or more.
decrypting all those url at once take to much time so i would like to do it the moment `XamarinMediaManager` try to play the `MediaItem`.

If the `MediaItem` Url need decrypting then i would do so otherwise i would just return the same `MediaItem`

### Platforms affected (mark all that apply)
- [x] :robot: Android
- [x] :monkey: Xamarin.Forms

No files, tests, or concrete entry points are named. Start by locating where XamarinMediaManager begins playback for a MediaItem, then trace how Android and Xamarin.Forms share that flow. Done means a global resolver can run immediately before playback, transform or decrypt the URI when needed, and leave an already usable MediaItem unchanged.

Written by the indexing model from the issue text.