Function migrate

pub(crate) async fn migrate(
    state: &mut CatalogState,
    tx: &mut Transaction<'_>,
    local_expr_cache: &mut LocalExpressionCache,
    item_updates: Vec<StateUpdate>,
    now: NowFn,
    _boot_ts: Timestamp,
) -> Result<MigrateResult, Error>

Migrates all user items and loads them into state.

Returns the builtin updates corresponding to all user items.