SDK / exoplayer

This uses `@hide` on `protected final` methods to hide them from Dackka
javadoc generation, since these methods are inaccessible to developers
anyway. These symbols will still (currently) be included in artefacts
distributed on Maven (because we don't run Metalava as part of
generating these artefacts).

In some cases I had to change the visibility/finality of methods to make
them `protected final` before adding the `@hide` annotation (but
the impact should be very low, since most of these methods were either
already unusable by app developers, or they shouldn't have been used).

#minor-release

PiperOrigin-RevId: 487472907