fix(android): fixes selectedTextTrack type 'index' only ever matching the first track

[evoactivity]

Summary

On Android, selectedTextTrack={{type: 'index', value: N}} is a silent no-op for any N >= 1 (regression in 6.16.0, introduced by #4581 — verified via git log -S: the comparison first appears in that PR's commit, and v6.16.0 is the first tag containing it).

selectTextTrackInternal compares the requested index against trackIndex, the position inside each track group. Text tracks are typically mapped as one single-track group each, so trackIndex is 0 for every group: only index 0 can ever match. Selecting any other index clears existing overrides, logs Text track not found for type=index … Keeping current selection, and applies nothing. If the stream has a default-flagged text track, it keeps rendering, which makes the failed selection easy to miss.

Meanwhile getTextTrackInfo numbers the tracks it reports through onTextTracks with a flat running position across all groups — so the index a JS app reads from onTextTracks and feeds back into selectedTextTrack never referred to the same track the selection side was looking for. (Before #4581, index selection resolved a track-group index, which matches the reported numbering for the common one-track-per-group mapping.)

Changes

Count a flat position across all groups and their tracks in selectTextTrackInternal, and match "index" against it — the same numbering getTextTrackInfo reports to JS. language and title matching are untouched.

Test plan

Any stream with 2+ text tracks reproduces it. A convenient source is fakestream, which generates synthetic test streams: fakestream serve, then play http://localhost:8080/vod/multilingual.mkv (four SubRip tracks: eng, fra, spa, jpn, each cue prefixed [EN]/[FR]/[ES]/[JA] so the active track is visible at a glance). On a device or emulator, bridge the port first with adb reverse tcp:8080 tcp:8080, and use cleartext-permitted debug builds since the URL is plain http.

• Before: {type: 'index', value: 1} leaves the previous track rendering (or the default-flagged track), with Text track not found … Keeping current selection in logcat
• After: indexes 0–3 each select and render their track; selected in onTextTracks follows
• {type: 'disabled'} and {type: 'language'} behave as before