finished the implementation of ShellCommands, upto printing the history and deleting ADTs

[jurgenvinju]

Because the syntax of these ShellCommands existed but they were not implemented, documented features would throw weird exceptions.

This PR:

• adds optional semicolons to the end of all : commands because I kept typing them accidentally
• implements the missing features :undeclare, :unset, :unimport, :unextend, :declarations, :clean
• prints a NYI message for :history which needs a little more wiring (@DavyLandman your advice on this pls)
• parametrizes :test with an optional module name (to run only the tests in that module)
• adds "undeclaration" features to the internal data-structures Environment and ModuleEnvironment of the interpreter. These work only well for the toplevel REPL structure, since normal modules can have complex states due to transitive extend and watch/reloading effects.

[codecov]

Codecov Report

Attention: Patch coverage is 11.73815% with 391 lines in your changes missing coverage. Please review.

Project coverage is 47%. Comparing base (0ca1613) to head (a8bf390).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/org/rascalmpl/ast/ShellCommand.java	0%	210 Missing ⚠️
.../org/rascalmpl/semantics/dynamic/ShellCommand.java	0%	81 Missing ⚠️
src/org/rascalmpl/ast/Sym.java	0%	25 Missing ⚠️
src/org/rascalmpl/ast/OptionalTerminator.java	0%	14 Missing ⚠️
src/org/rascalmpl/interpreter/env/Environment.java	0%	10 Missing ⚠️
src/org/rascalmpl/ast/Statement.java	66%	9 Missing ⚠️
src/org/rascalmpl/ast/Strategy.java	0%	6 Missing ⚠️
src/org/rascalmpl/ast/NullASTVisitor.java	0%	4 Missing ⚠️
src/org/rascalmpl/ast/StringTemplate.java	20%	4 Missing ⚠️
src/org/rascalmpl/ast/SyntaxDefinition.java	0%	4 Missing ⚠️
... and 15 more

Additional details and impacted files

@@           Coverage Diff            @@
##              main   #2311    +/-   ##
========================================
- Coverage       47%     47%    -1%     
+ Complexity    6347    6344     -3     
========================================
  Files          764     765     +1     
  Lines        63176   63557   +381     
  Branches      9428    9489    +61     
========================================
+ Hits         29957   29974    +17     
- Misses       31000   31357   +357     
- Partials      2219    2226     +7     

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