This change renames the existing `sample_with_ssa_subtitles.mkv` test
file (with `S_TEXT/ASS` codec ID) to `sample_with_ass_subtitles.mkv`
(so the file name matches the codec ID), and forks a new test file
called `sample_with_ssa_subtitles.mkv` with the `S_TEXT/SSA` codec ID.
`MatroskaExtractorTest` then asserts that both these files produce
identical dump files.
Issue: androidx/media#2384
PiperOrigin-RevId: 753164883
c137d27850