Allow setting AVPlayer

[SpartanRASUL]

Hello. In my previous work, I've run into a problem, where I needed to change standard AVPlayer to AVQueuePlayer, because of it's prefetching feature. So to fix that I usually change the header file with this exact change. I think it may come in handy to other developers, who may want to use AVQueuePlayer instead of AVPlayer.

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[jparise]

We could instead remove the readonly attribute from the player property:

@property (nullable, readonly) AVPlayer *player;

[jparise]

We could instead remove the readonly attribute from the player property:

@property (nullable, readonly) AVPlayer *player;

[SpartanRASUL]

@jparise Yeah, really

[SpartanRASUL]

i'll update this pull request soon