Update some text descriptions to ease translations.
Update some text descriptions to ease translations.

Some strings didn't mention the context in which they are used
(for example as item in a list, or for accessibility). This makes it
harder for translators to choose the most appropriate translation and
grammar.

Also fix repeat and shuffle mode button accessibility descriptions to
indicate the action, not the current state.

PiperOrigin-RevId: 426924163

google/ExoPlayer,androidx/media,androidx/media,amzn/exoplayer-amazon-port,amzn/exoplayer-amazon-port,androidx/media,google/ExoPlayer,google/ExoPlayer,amzn/exoplayer-amazon-port