Make typed ClassType interface same as FunDef

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

src/main/scala/leon/purescala/Definitions.scala

src/main/scala/leon/purescala/ExprOps.scala

src/main/scala/leon/purescala/MethodLifting.scala

src/main/scala/leon/purescala/Types.scala

src/main/scala/leon/termination/StructuralSize.scala

src/test/scala/leon/test/purescala/DataGenSuite.scala