This removes concurrent access from `rtspLoaderWrappers`. Previously
there was a race between the playback thread clearing & re-adding
entries to this list in `retryWithRtpTcp()`, and the loading thread
accessing the entries in `InternalListener.track()` (implemented from
`ExtractorOutput`).
This change means each `ExtractorOutputImpl` uses exactly one
`SampleQueue` for its one `TrackOutput`. When the `RtspLoaderWrapper`
instances are replaced in `retryWithRtpTcp()`, any stale instances will
only be able to access their own (also stale) `SampleQueue` instances
(vs before, where the stale `ExtractorOutput` could accidentally access
'new' `SampleQueue` instances via the `rtspLoaderWrappers` field).
As well as fixing a race condition in the prod code, this also de-flakes
`RtspPlaybackTest`.
#minor-release
PiperOrigin-RevId: 559130479
9533f5cd1c