added implementation of negative number matching.

[jurgenvinju]

@PaulKlint couldn't help it. This can wait until we find it a good moment. The implementation is very simply to check if the subject is a negative number or not.

[codecov[bot]]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (8e0f7b2) 49% compared to head (7a13680) 49%.

Files	Patch %	Lines
...ascalmpl/interpreter/matching/NegativePattern.java	0%	5 Missing :warning:
...rc/org/rascalmpl/semantics/dynamic/Expression.java	0%	4 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##              main   #1914   +/-   ##
=======================================
- Coverage       49%     49%   -1%     
- Complexity    6164    6166    +2     
=======================================
  Files          661     661           
  Lines        58702   58708    +6     
  Branches      8547    8549    +2     
=======================================
+ Hits         28962   28964    +2     
- Misses       27550   27552    +2     
- Partials      2190    2192    +2     

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