SDK / exoplayer

ShadowLooper -> ShadowLegacyLooper
ShadowRealisticLooper -> ShadowPausedLooper
ShadowBaseLooper -> ShadowLooper

And all public methods from ShadowLegacyLooper get pushed up to ShadowLooper

Pull Request: https://github.com/robolectric/robolectric/pull/4868

Copybara: OK

Also adjust Google3 tests  using custom looper shadows where necessary.
Convert exoplayer to paused looper to eliminate reliance on custom shadows

PiperOrigin-RevId: 243839311