Add JSON.parse utility to the "jexl function library"

[cmdcolin]

This adds a JSON.parse utility to the jexl functions. It is a little specialized but this can enable a sort of (office hours) use case where a table of data can be stored in a GFF3 attribute as a json "array of objects". A volvox track showing this use case is added in this PR too

The alternative is that this isn't a built in utility but doesn't seem too bad to add it

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.59%. Comparing base (ddae2c9) to head (3e7b49c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4280      +/-   ##
==========================================
- Coverage   62.66%   62.59%   -0.07%     
==========================================
  Files        1088     1088              
  Lines       31459    31460       +1     
  Branches     7515     7515              
==========================================
- Hits        19713    19692      -21     
- Misses      11568    11591      +23     
+ Partials      178      177       -1     

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[cmdcolin]

should be harmless enough :)