Validate encoders using MediaCodecList

[selsamman]

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It seems that validation of encoders was hard coded rather than using MediaCodecList. In the case of passthrough transcoding this can cause failures. This was cherry-picked from my fork which has tests and all tests ran with this code. I did not test it with the upstream repo.

[selsamman]

This relates to https://github.com/ypresto/android-transcoder/issues/76

[jonmaim]

Thanks @selsamman, great commit!

[ypresto]

Thats validation is intended: combinations of container x video-codec x audio-codec are so many but has limitation. Also uncommon combinations are not guaranteed to be supported on all (most of) devices.

Since this library is intended to generate video with stable format, I prefer common, frequently used combination for stability.