Add adaptive track format comparator with safe fallback

[AndyWangLYN]

Summary

This PR adds optional custom format ordering for AdaptiveTrackSelection so apps can influence ABR priority beyond bitrate-only ordering.

This PR is refined version of the PR: #3064 in which I received comments about track format sorting. Intend to close above PR if this one is deemed good eventually.

What changed

• Added AdaptiveTrackSelection.Factory#setTrackFormatComparator(Comparator).

• Plumbed comparator through adaptive selection construction.

• Added protected constructor support so AdaptiveTrackSelection subclasses can pass a comparator.

• Kept existing default ordering (bitrate descending) when no comparator is provided.

• Added safety fallback: if comparator sorting throws any error, ordering falls back to default bitrate-desc behavior.

• Updated track selection docs to clarify that order is “selection order” (default remains bitrate-desc).

Why

Current adaptive selection effectively prioritizes higher bitrate first. This makes it hard to prioritize developer-defined rules (for example, quality score ranking). These hooks allow custom ordering without changing core ABR switching logic.

Testing Done

• Unit test for comparator and default behavior

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.