fix: Ensure native segment metadata track has mode hidden

[mister-ben]

Description

When using native text tracks, the segment metadata track was being created with mode disabled. This meant it wouldn't trigger cuechange events, but also Chrome (at least) does not add cues to disabled tracks. This change makes the track start out hidden.

Specific Changes proposed

• Set mode to hidden
• Adds a simple test for track mode. Testing whether the cues are added isn't simple as addSegmentMetadataCue_ is made noop in the tests.
• Adds native text tracks as an option to the text page for manual verification.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (main@9f1c4ad). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1550   +/-   ##
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  Coverage        ?   84.06%           
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  Files           ?       43           
  Lines           ?    11628           
  Branches        ?     2604           
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  Hits            ?     9775           
  Misses          ?     1853           
  Partials        ?        0           

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[phloxic]

typo in commit message: s/mdoe hidden/mode hidden/