addTrackSelectionForSingleRenderer takes a list of legacy overrides,
which are then set on the supplied parameters one at a time to run
track selection. This allows multiple overrides for a single track
type to be applied in the download use case, despite it not being
possible to place such overrides directly into a single parameters.
For new style overrides, multiple overrides for the same track type
can be placed directly into a single parameters. Therefore we'll be
able to replace use of addTrackSelectionForSingleRenderer with use
of addTrackSelection, which is a much cleaner API. For this to work,
we need to make DownloadHelper apply multiple overrides in this case.
PiperOrigin-RevId: 432459834
