`prepare()` now logs a warning if it's called before `setPlayer()`
because it's not possible to tell if it's being called on the wrong
thread (since https://github.com/androidx/media/commit/3480a27994ef9e06bd7574bad4656eb8c7677971).
This change finds all the places one is called immediately after the
other and flips the order to be more correct.
Issue: androidx/media#350
#minor-release
PiperOrigin-RevId: 526582294
