[video_player] Adding support for preferred audio language

[frontyard]

Added support for preferred audio language to video_player on Android. If underlaying stream/video supports it this will communicate to exoplayer that audio stream for sepcific language should be used if available.

To use this feature developer should pass preferredAudioLanguage as a 2 character ISO langauge code to VideoPlayerOptions when initializing VideoPlayerController. This code should match one of the language specified in the stream, for example (HLS):
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio",NAME="Italian",LANGUAGE="it",DEFAULT=NO,AUTOSELECT=YES,URI="audio/italian.m3u8"

Platforms that don't have implementation yet will silently ignore this.

This PR implements flutter/flutter#166411

Pre-Review 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.
• 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 I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

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Footnotes

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[camsim99]

Hi, thank you for your contribution! This looks like a great feature to support, but it looks like the tests are failing. Before we review the PR, please see what you can do to resolve the test failures. If you are unsure how to proceed, please reach out for help on the #hackers-new channel.

[frontyard]

@camsim99 sorry about that, my first packages PR, still wrapping my head around it. I've updated the code and fixed the tests, flutter test is now passing in all the submodules.

[stuartmorgan-g]

Please see step 1 of the instructions for multi-package PRs for the instructions on how to make this PR something that the CI can run tests on without failing all of the checks.

[frontyard]

@stuartmorgan-g followed the instructions and updated pubspecs to use local path dependencies.

[stuartmorgan-g]

Thanks; it looks like CI is now flagging a number of real failures caused by the PR (analysis, Android lint, macOS native tests). The "View details" links for the failing tests will lead to the stdout of the failures.