awaitForHasElementStack property
Whether each nested await-for loop currently holds an unconsumed element.
Parallel to awaitForNodeStack. The loop's handler is re-entered both
after a moveNext() resumption and after its body finishes, and this is
what tells those apart: with an element in hand it binds and runs the
body, without one it asks for the next.
Implementation
final List<bool> awaitForHasElementStack = [];