lent doesn't work in js iterators for most types

[timotheecour]

Example 1

when true:
  template main =
    iterator fn[T](a:T): lent T = yield a
    let a = @[10]
    for b in fn(a): echo b

  static: main()
  main()

Current Output

js+vm: @[10]
js+rt: @[]

Expected Output

js+vm: @[10]
js+rt: @[10]

Example 2

likewise, js+rt is broken with the following:

    # bugs:
    let a = "abc"
    # let a = "abc".cstring
    # let a = 12

    # ok:
    # let a = [1,2]
    # let a = (1,2)

a test fixing this should cover all those, and ideally more types.

Additional Information

1.5.1 fa9dc31