Interpreter does not support sub-typing for regular symbols with type parameters

[jurgenvinju]

Describe the bug

This is never called:

int size({&E &S}* l) = (0 | it + 1 | _ <- l);

because the parameter type does not match:

rascal>size((Pattern) `f(1,2,3)`.arguments)
|prompt:///|(5,30,<1,5>,<1,35>): CallFailed([appl(
      regular(\iter-star-seps(
          sort("Pattern"),
          [

This is already witnessed by a simpler assignment:

rascal>{&Elem &Sep}* l = (Pattern) `f(1,2,3)`.arguments;
)
|prompt:///|(14,34,<1,14>,<1,48>): Expected {&Elem &Sep}*, but got {Pattern ","}*
Advice: |https://www.rascal-mpl.org/docs/Rascal/Errors/CompileTimeErrors/UnexpectedType|

This is problematic. If you want to deal with syntax lists the support in Rascal is (too) minimal. I need functions like size and zip2.

[jurgenvinju]

It looks like the .isSubtype method on NonterminalType is broken.

  if (SymbolAdapter.isParameter(otherSym)) {
		  RascalType bound = (RascalType) RTF.nonTerminalType((IConstructor) otherSym.get("bound"));
		  return isSubtypeOf(bound);
	  }

This returns a bound Tree but not an adt with the name "Tree" but a syntax sort named "Tree". That is causing the trouble. So the question is how this bound dropped in.