more robust handling of proc signatures containing inter-param type references

tests/generics/tsigtypeop.nim

@@ -0,0 +1,9 @@
+type
+  Vec3[T] = array[3, T]
+
+proc foo(x: Vec3, y: Vec3.T, z: x.T): x.type.T =
+  return 10
+
+var y: Vec3[int] = [1, 2, 3]
+var z: int = foo(y, 3, 4)
+