Forced subtitle DASH support checking for wrong Role@value

[theRealRobG]

Have you read the FAQ and checked for duplicate open issues?
Yes

What version of Shaka Player are you using?
3.2.1

Can you reproduce the issue with our latest release version?
Yes

Can you reproduce the issue with the latest code from master?
Yes

Are you using the demo app or your own custom app?
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If custom app, can you reproduce the issue using our demo app?
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For embedded devices (smart TVs, etc.), what model and firmware version are you using?
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What configuration are you using? What is the output of player.getConfiguration()?

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What did you do?

The 4th edition of ISO/IEC 23009-1 (publicly available here) has this change:

the ability to signal forced subtitles, easyreader and karaoke in the DASH Role scheme was added;

Shaka added support for forced narrative signalling from DASH in #2938.

What did you expect to happen?
The signalling of forced narrative track would be detected via roles.includes('forced-subtitle');.

This is defined in Table 31 — Role@value attribute for scheme with a value "urn:mpeg:dash:role:2011"

Role@value	Description	Applicable Media Type(s) (Informative)
forced-subtitle	Textual information meant for display when no other text representation is selected. It is used to clarify dialogue, alternate languages, texted graphics or location/person IDs that are not otherwise covered in the dubbed/localized audio.	text

What actually happened?

The signalling of forced narrative track is detected via roles.includes('forced_subtitle');.