MediaItems are not meant to be unique in a playlist. If a legacy
session publishes multiple items that get converted to equal MediaItems,
the current code fails because we look up queue ids in a Map (that
doesn't allow duplicate entries).
Fix this by storing a simple list of items with additional data.
Issue: androidx/media#290
PiperOrigin-RevId: 521993802
(cherry picked from commit 219967c5)
