Add Format.selectionPriority and parse from HLS SCORE

[AndyWangLYN]

Summary

Adds Format.selectionPriority and populates it from the HLS SCORE attribute on EXT-X-STREAM-INF /
EXT-X-I-FRAME-STREAM-INF.

Extraction-only — no selection behavior changes. Apps that want ABR to honor the field can install a
Comparator<Format> via AdaptiveTrackSelection.Factory#setTrackFormatComparator (#3068).

DASH @selectionPriority parsing follows in a separate PR.

Spec

draft-pantos-hls-rfc8216bis-22 §4.4.6.2
(SCORE on EXT-X-STREAM-INF), §4.4.6.3 (inherits to EXT-X-I-FRAME-STREAM-INF), §6.3.1 (client behavior).

Notes for reviewers

• setSelectionPriority doesn't validate inputs — matches Format Builder convention (grep -n "checkArgument" Format.java returns zero hits).
• Field Javadoc mentions DASH for completeness; happy to defer that sentence to the DASH follow-up PR if preferred.

Test plan

• ./gradlew :lib-common:test
• ./gradlew :lib-exoplayer-hls:connectedAndroidTest
• git diff -U0 main... | google-java-format-diff.py -p1 -i