[video_player_avfoundation] Support the audio-only HLS (.m3u8) on iOS

[napoleon-na]

Supports the audio-only HLS on iOS.

After through flutter/plugins#4639 and flutter/plugins#4727, we can play HLS videos and audios, but it does not support audio-only HLS. When attempting to play that on iOS, it never finishes initialization.

Show the before/after demonstration here: flutter/flutter#156589 (comment)

Fixes: flutter/flutter#156589
Test with flutter/assets-for-api-docs#252

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or this PR is exempt from CHANGELOG changes.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

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[napoleon-na]

I would appreciate checking flutter/assets-for-api-docs#252 first to pass the tests in this PR. Although I read the docs, let me know if I need to go through a different process.