FragmentChecker complains when a case class parameter has the same name as inherited members

[mario-bucev]

Originally discovered by @agilot
In the following:

object FragmentChecker {
  case class Test(eq: Int)
}

The FragmentChecker will reject the snippet with the following error:

[ Error  ] FragmentChecker.scala:2:18: Non-field constructor parameters are not allowed in Stainless.
             case class Test(eq: Int)
                            ^^^^^^^^^

It is due to eq having the same name as the method eq inherited from Any.