added optional storage of constructor names and datatype names while serializing to JSON. Wired this through the different webservers as well

[jurgenvinju]

This adds explicitConstructorNames and explicitDataType as keyword parameters to the JSON readers and writers. An constructor foo(bar(), what()) will be printed as such when explicitConstructorNames=true:

{
   _constructor = "foo",
   lhs = { 
      _constructor = "bar"
   },
   rhs = {
      _constructor = "what"
   }
}

This facilitates mapping syntax trees to JSON.

[codecov]

Codecov Report

Merging #1862 (4c57b8d) into main (d55cb74) will decrease coverage by 1%.
The diff coverage is 10%.

@@           Coverage Diff           @@
##              main   #1862   +/-   ##
=======================================
- Coverage       49%     49%   -1%     
- Complexity    6105    6107    +2     
=======================================
  Files          670     670           
  Lines        58756   58807   +51     
  Branches      8555    8568   +13     
=======================================
+ Hits         28809   28816    +7     
- Misses       27753   27797   +44     
  Partials      2194    2194           

Files Changed	Coverage Δ
...pl/library/lang/json/internal/JsonValueWriter.java	0% <0%> (ø)
src/org/rascalmpl/library/util/TermREPL.java	0% <0%> (ø)
src/org/rascalmpl/library/util/Webserver.java	0% <0%> (ø)
src/org/rascalmpl/repl/REPLContentServer.java	0% <0%> (ø)
...pl/library/lang/json/internal/JsonValueReader.java	16% <19%> (+<1%)	⬆️
src/org/rascalmpl/library/lang/json/IO.java	39% <25%> (-2%)	⬇️

... and 7 files with indirect coverage changes

[jurgenvinju]

this requires some tests to be added. other than that it seems to do the job.