Summary

• Parse DASH selectionPriority on AdaptationSet and Representation into Format.selectionPriority.
• Preserve DASH inheritance semantics: representations inherit from their parent adaptation set, defaulting to 1 when absent.
• Add DASH parser coverage with a small MPD fixture.

This follows the merged HLS SCORE extraction in #3236 .

Official public ISO DASH MPD schema: https://standards.iso.org/iso-iec/23009/-1/ed-3/en/DASH-MPD.xsd

Testing

• ./gradlew :lib-common:assemble :lib-exoplayer-dash:assemble
• git diff --check