Add `&` pattern

[CoffeeTableEspresso]

so something like

match x {
    let x & [ ... ] {
        echo "list: #{x}"
    }
    * {
        echo 'not a list'
    }
}

This should have tighter precedence than | and also allow () for grouping, so x & y | z (for patterns x, y, z) is the same as (x & y) | z.