Set type of object constructor during annotateType (#23852)

Fix #23547

Tested locally with the included test, the test from constantine and the
original issue.

compiler/semmacrosanity.nim

@@ -51,6 +51,7 @@ proc annotateType*(n: PNode, t: PType; conf: ConfigRef) =
   of nkObjConstr:
     let x = t.skipTypes(abstractPtrs)
     n.typ = t
+    n[0].typ = t
     for i in 1..<n.len:
       var j = i-1
       let field = x.ithField(j)

tests/macros/t23547.nim

@@ -0,0 +1,23 @@
+# https://github.com/nim-lang/Nim/issues/23547
+
+type
+  A[T] = object
+    x: T
+
+proc mulCheckSparse[F](dummy: var A[F], xmulchecksparse: static A[F]) =
+  static:
+    echo "mulCheckSparse: ", typeof(dummy), ", ", typeof(xmulchecksparse) # when generic params not specified: A[system.int], A
+
+template sumImpl(xsumimpl: typed) =
+  static:
+    echo "sumImpl: ", typeof(xsumimpl) # A
+  var a = A[int](x: 55)
+  mulCheckSparse(a, xsumimpl) # fails here
+
+proc sum[T](xsum: static T) =
+  static:
+    echo "sum: ", typeof(xsum) # A[system.int]
+  sumImpl(xsum)
+
+const constA = A[int](x : 100)
+sum[A[int]](constA)