set the tuple syntax to a plus list again, with corresponding changes in calls to getters

[jurgenvinju]

This should undo the cause for #2133 without fixing the underlying issue.

• We need this revert because the current interpreter is unable to boot the next version of the type-checker.
• Ignore any test functions that accept value as a parameter, since empty tuples can be generated which we can't
  write matching or expression code against. In particular the JSON tests must be made quiet until we fix Plus list variable not accepted in Star list position in concrete syntax #2133 for real.

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 50%. Comparing base (14ecaa6) to head (61f2ff2).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/org/rascalmpl/ast/Expression.java	62%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              main   #2134   +/-   ##
=======================================
- Coverage       50%     50%   -1%     
- Complexity    6243    6245    +2     
=======================================
  Files          673     673           
  Lines        58830   58844   +14     
  Branches      8599    8599           
=======================================
- Hits         29577   29539   -38     
- Misses       27020   27065   +45     
- Partials      2233    2240    +7     

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[jurgenvinju]

Let's keep this branch around so we can revert the commits as soon as issue #2133 is truly fixed.

[DavyLandman]

@jurgenvinju how about you open a draft PR with the revert?