SDK / exoplayer

This avoids that apps have to depend on the legacy compat support
library when they want to make this conversion.

Also add a version to both helper methods that takes a Looper to
give apps the option to use an existing Looper, which should be
much faster than spinning up a new thread for every method call.

Issue: androidx/media#171
PiperOrigin-RevId: 490441913
(cherry picked from commit 03f0b53c)