issue 2149 mvn scheme

[jurgenvinju]

• the root of a file system should be a folder; for the mvn scheme it was both a folder and a file
• simplified the tests accordingly, no more
• finished a true mvn:/// resolver that is not hampered by the limitations of a logical resolver, including proper listing of authorities and a proper ClassLoader factory method
• cleaning up

[DavyLandman]

Some small remarks, mostly looks like we discussed

[codecov]

Codecov Report

Attention: Patch coverage is 27.84810% with 57 lines in your changes missing coverage. Please review.

Project coverage is 50%. Comparing base (bf583ae) to head (56523de).
Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
...rascalmpl/uri/file/MavenRepositoryURIResolver.java	25%	46 Missing and 2 partials ⚠️
src/org/rascalmpl/library/util/Maven.java	30%	3 Missing and 6 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              main   #2159   +/-   ##
=======================================
- Coverage       50%     50%   -1%     
- Complexity    6578    6585    +7     
=======================================
  Files          699     699           
  Lines        60711   60739   +28     
  Branches      8886    8886           
=======================================
+ Hits         30415   30418    +3     
- Misses       28047   28062   +15     
- Partials      2249    2259   +10     

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