async function _asyncNullishCoalesce(lhs, rhsFn) {
  return _nullishCoalesce._nullishCoalesce(lhs, rhsFn);
}
Polyfill for the nullish coalescing operator (`??`), when used in situations where at least one of the values is the
result of an async operation.

Note that the RHS is wrapped in a function so that if it's a computed value, that evaluation won't happen unless the
LHS evaluates to a nullish value, to mimic the operator's short-circuiting behavior.

Adapted from Sucrase (https://github.com/alangpierce/sucrase)

@param lhs The value of the expression to the left of the `??`
@param rhsFn A function returning the value of the expression to the right of the `??`
@returns The LHS value, unless it's `null` or `undefined`, in which case, the RHS value