1. Prefer label and language values in the manifest to those in
the media. This is particularly helpful if the sample format
contains "und" as the language.
2. Copy label when deriving formats in HlsSampleStreamWrapper
3. When there's only one variant in HlsSampleStreamWrapper, use
the regular copyWithManifestFormatInfo. This allows more
information to be retained from the sample format.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=204340008
18ab4b9112