chore: add contrib-eme errors

[adrums86]

Description

Add error constants for contrib-eme specific errors.

Specific Changes proposed

Add constants that are representative of the separate keysystems for error reporting out of videojs-contrib-eme, also add errors specific to each step in the EME specific process.
Two notable omissions:
No errors for remove or load on the mediakeysession as they're not implemented in contrib-eme.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • 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 ✅

Project coverage is 82.71%. Comparing base (9977a93) to head (1e6d5e7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8634      +/-   ##
==========================================
- Coverage   83.43%   82.71%   -0.73%     
==========================================
  Files         113      113              
  Lines        7636     7636              
  Branches     1835     1835              
==========================================
- Hits         6371     6316      -55     
- Misses       1265     1320      +55     

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[wseymour15]

🚀

[dzianis-dashkevich]

Could you elaborate more on this 3:

What are they?
Why do we need them?

  EMEEncryptedError: 'eme-encrypted-error',
  MSKeyError: 'ms-key-error',
  WebkitKeyError: 'webkit-key-error',

[adrums86]

The idea behind these 3 was to be a catch-all for the outermost promise to the respective handle events. For MSKeyError and WebkitKeyError they specifically cover errors from legacy workflows ('msneedey' and 'webkitneedkey' events). Since this is not really in-spec EME, I figured they were worthy of their own specific errors. For EMEEncryptedError it might not be necessary and was only added incase any other type of unknown error occurs and bubbles up to the handleEncryptedEvent promise.