Maybe we can add a Collect API to avoid strange patterns?

[Xuanwo]

For now, we often write codes like:

fn.Body(gg.Embed(func() gg.Node {
	i := gg.Return()
	iv := i.Value("Pair")
	iv.Field("Key", pair.Name)
	iv.Field("Value", "v")
	return i
}))

It's because gg.Return().Value() returns a *ivalue, so we can't write like:

gg.Return().
    Value().
    Field("Key", pair.Name).
    Field("Value", "v")

How about adding a Collect which returns the parent Node of the current one? So that we can write like this:

fn.Body(
    gg.Return().
        Value().
        Field("Key", pair.Name).
        Field("Value", "v").
    Collect())