C#: Let the params test look in reference assemblies and update param…

…s to allow ParamsCollectionType.

csharp/ql/test/library-tests/methods/Parameters4.ql

@@ -3,6 +3,7 @@
  */
 
 import csharp
+import semmle.code.csharp.commons.Collections
 
-where forall(Parameter p | p.isParams() and p.fromSource() | p.getType() instanceof ArrayType)
+where forall(Parameter p | p.isParams() | p.getType() instanceof ParamsCollectionType)
 select 1