Add support for return programs

[westonpace]

Some Substrait functions can feature "return programs" which are small programs that must be run to calculate the return type. For example:

    name: "add"
    description: "Add two decimal values."
    impls:
      - args:
          - name: x
            value: decimal<P1,S1>
          - name: y
            value: decimal<P2,S2>
        options:
          overflow:
            values: [ SILENT, SATURATE, ERROR ]
        return: |-
          init_scale = max(S1,S2)
          init_prec = init_scale + max(P1 - S1, P2 - S2) + 1
          min_scale = min(init_scale, 6)
          delta = init_prec - 38
          prec = min(init_prec, 38)
          scale_after_borrow = max(init_scale - delta, min_scale)
          scale = init_prec > 38 ? scale_after_borrow : init_scale
          DECIMAL<prec, scale>

We should be able to add function builders for these functions and should be able to calculate the return type correctly.