Function generate_with_overlay_inner_unordered 

pub fn generate_with_overlay_inner_unordered<'g, I: Iterator<Item = OwnedRow> + 'g>(
    inner: I,
    overlays: Overlays,
    primary_key: Vec<ColId>,
) -> RowFlow<'g>

Splice already-computed overlays into an unordered row stream. Exposed for the JS generateWithOverlayInnerUnordered suite.