more arc features (#13098)

* config update
* ARC now supports 'repr' and 'new' with finalizers is supported

tests/destructor/tfinalizer.nim

@@ -0,0 +1,25 @@
+discard """
+  cmd: "nim c --gc:arc $file"
+  output: '''Foo(field: "Dick Laurent", k: ka, x: 0.0)
+Dick Laurent is dead'''
+"""
+
+type
+  Kind = enum
+    ka, kb
+  Foo = ref object
+    field: string
+    case k: Kind
+    of ka: x: float
+    of kb: discard
+
+#var x = Foo(field: "lovely")
+proc finalizer(x: Foo) =
+  echo x.field, " is dead"
+
+var x: Foo
+new(x, finalizer)
+x.field = "Dick Laurent"
+# reference to a great movie. If you haven't seen it, highly recommended.
+
+echo repr x