Implement into IntoArrowNumericType trait

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
We are trying to implement more generic "scalar" kernels -- see discussion on #984

If one wants to call eq_scalar on a PrimtiveArray,

    let array: Int8Array = vec![1,2,3]
        .into_iter()
        .map(Some)
        .collect();

    let comparison = arrow::compute::eq_scalar(&array, 2).unwrap();

    let expected: BooleanArray = vec![false, true, false]
        .into_iter()
        .map(Some)
        .collect();

    assert_eq!(comparison, expected);

In this case, since the data type (Int8Type ) is an associated type of the PrimitiveArray type, Rust can infer the correct type for argument 2 into the 2i8 needed for calling eq_scalar.

However as soon as you have an ArrayRef (aka dynamic array), it becomes challenging. To write a generic "compare this array to a scalar value" we would liek to write something like this:

/// Perform `left == right` operation on an array and a numeric scalar
/// value. Supports PrimtiveArrays, and DictionaryArrays that have primitive values
pub fn eq_dyn_scalar<T>(
    left: &dyn Array,
    right: T::Native,
) -> Result<BooleanArray>
where
    T: ArrowNumericType,
{
...
}

However, to actually call this function, the type of right needs to match T, but there is a potentially infinite number of concrete T types that could have a matching associated type Native, as explained by @shepmaster in #984 (comment)

Practically that means that all calls to eq_dyn_scalar would require type annotations which matched the values of the array, which largely defeats the purpose of eq_dyn_scalar

        let array = builder.finish();
        // still need the UInt8Type annotations
        let a_eq = eq_dyn_scalar::<UInt8Type>(&array, 123u8).unwrap();
        assert_eq!(
            a_eq,
            BooleanArray::from(vec![Some(true), None, Some(false)])
        );

Describe the solution you'd like

So the proposal from @shepmaster at #984 (comment) is to add a trait that maps in the reverse direction, so we could have something like:

struct UInt8Type;
struct Int64Type;
struct DictionaryArray<K>(K);

// ----

trait ArrowNumericType {
    type Native;
}

trait IntoArrowNumericType {
    type Arrow: ArrowNumericType<Native = Self>;
}

// ----

impl ArrowNumericType for UInt8Type {
    type Native = u8;
}

impl IntoArrowNumericType for u8 {
    type Arrow = UInt8Type;
}

impl ArrowNumericType for Int64Type {
    type Native = i64;
}

impl IntoArrowNumericType for i64 {
    type Arrow = Int64Type;
}

// ----

fn eq_dict_scalar<K, T>(left: &DictionaryArray<K>, right: T)
where
    K: ArrowNumericType,
    T: IntoArrowNumericType,
{
    todo!()
}

// ----

fn usage<K>(d: &DictionaryArray<K>)
where
    K: ArrowNumericType,
{
    eq_dict_scalar(d, 8u8);
    eq_dict_scalar(d, -64i64);
}

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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[alamb]

I think we have decided on a different approach for #1074 so closing this ticket