feat/error recovery robust field projection

[jurgenvinju]

This experiment makes parse tree instances (ITree's in Java) which happen to have error productions robust again field projection (in the interpreter)

• if the field is before the error "dot", it just works as normal field projection
• if the field is on or beyond the error dot, then we return a fresh error tree of the right type but without content.

Of course further field projection on such a stub would not work anymore, because there is no more production to work with. So this gives only one layer of robustness. A future version of this could recursively keep returning empty error stubs, but I don't know how to obtain the right type for those trees from the interpreter.

The questions are:

• does this help to remove many scattered hasError checks?
• is this predictable and understandable behavior for the field projection semantics?
• @PaulKlint compiled version of tree field projection {sh,w,c}ould also have this semantics?
• what did I forget?

At the very least field projection should work for fields which are before the dot. The rest is open for discussion I think.

[codecov]

Codecov Report

Attention: Patch coverage is 11.90476% with 37 lines in your changes missing coverage. Please review.

Project coverage is 49%. Comparing base (415773f) to head (e964a65).
Report is 20 commits behind head on feat/error-recovery.

Files with missing lines	Patch %	Lines
...c/org/rascalmpl/values/parsetrees/TreeAdapter.java	0%	23 Missing ⚠️
...almpl/interpreter/result/ConcreteSyntaxResult.java	0%	10 Missing ⚠️
...rascalmpl/values/parsetrees/ProductionAdapter.java	55%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##             feat/error-recovery   #2073   +/-   ##
=====================================================
- Coverage                     49%     49%   -1%     
+ Complexity                  6605    6602    -3     
=====================================================
  Files                        685     685           
  Lines                      61148   61187   +39     
  Branches                    8850    8862   +12     
=====================================================
+ Hits                       30239   30243    +4     
- Misses                     28706   28740   +34     
- Partials                    2203    2204    +1     

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[jurgenvinju]

This PR now also covers has, is, setLabeledField on error trees next to the getLabeledField it was originally for.

• Some off-by-one errors wrt the dot to look out for
• this needs a lot of tests