[Feature] Add preferredAudioChannelCount for audio track selection

[KanghyunJeon]

Summary

This PR implements the feature requested in #2992.

Adds a new TrackSelectionParameters.preferredAudioChannelCount API that allows apps to prefer audio tracks with higher channel counts (e.g., 5.1, 7.1 surround) over stereo tracks, regardless of role flags (main vs alternate).

Changes

• Add preferredAudioChannelCount field to TrackSelectionParameters
• Add setPreferredAudioChannelCount(int) builder method
• Modify AudioTrackInfo.compareTo() to prioritize higher channel count when preference is set
• Reuse existing parameters and channelCount fields

Behavior

• When preferredAudioChannelCount > 0, tracks are compared by channel count before role flags
• Higher channel count tracks are preferred
• Falls back to lower channel count if higher is not supported by the renderer
• Set to 0 (default) to use original behavior based on role flags

Issue

#2992

[microkatz]

I'm going to send this for internal review now. You may see some more commits being added as I make changes in response to review feedback. Please refrain from pushing any more substantive changes as it will complicate the internal review - thanks!