Iter test: closes #3819 (#9272)

tests/iter/titer11.nim

@@ -0,0 +1,28 @@
+discard """
+  file: "titer11.nim"
+  output: '''[
+1
+2
+3
+]
+'''
+"""
+
+proc represent(i: int): iterator(): string =
+  result = iterator(): string =
+    yield $i
+
+proc represent(s: seq[int]): iterator(): string =
+  result = iterator(): string =
+    yield "["
+    for i in s:
+      var events = represent(i)
+      for event in events():
+        yield event
+    yield "]"
+
+let s = @[1, 2, 3]
+var output = represent(s)
+
+for item in output():
+  echo item