fixes #18081; fixes #18079; fixes #18080; nested ref/deref'd types (#24335)

fixes #18081;
fixes https://github.com/nim-lang/Nim/issues/18080
fixes #18079

reverts https://github.com/nim-lang/Nim/pull/20738

It is probably more reasonable to use the type node from `nkObjConstr`
since it is barely changed unlike the external type, which is
susceptible to code transformation e.g. `addr(deref objconstr)`.

tests/ccgbugs/t13062.nim

@@ -31,3 +31,39 @@ elif defined(gcRefc):
   doAssert x.repr == "[p = nil]"
 else: # fixme # bug #20081
   doAssert x.repr == "Pledge(p: nil)"
+
+block:
+  block: # bug #18081
+    type
+      Foo = object
+        discard
+
+      Bar = object
+        x: Foo
+
+    proc baz(state: var Bar) =
+      state.x = Foo()
+
+    baz((ref Bar)(x: (new Foo)[])[])
+
+  block: # bug #18079
+    type
+      Foo = object
+        discard
+
+      Bar = object
+        x: Foo
+
+    proc baz(state: var Bar) = discard
+    baz((ref Bar)(x: (new Foo)[])[])
+
+  block: # bug #18080
+    type
+      Foo = object
+        discard
+
+      Bar = object
+        x: Foo
+
+    proc baz(state: var Bar) = discard
+    baz((ref Bar)(x: Foo())[])