[Variant] Implement `VariantArray::value` for shredded variants

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

• part of [EPIC] [Parquet] Implement Variant type support in Parquet #6736

We introduced the basic variant_get kernel in and now we need to expand its feature set

• [Variant] Add variant_get and Shredded VariantArray #8021

The VariantArray::value method is supposed to return a Variant::Value at the relevant index. This currently works fine for Unshredded variants but for most shredded variants and will panic in debug buillds, and return a Variant::Null in release builds

@Samyak2 commented here: #8021 (comment)

That's unfortunate. Maybe a separate issue for that?

Describe the solution you'd like

I would like VariantArray::value to work for more value types

Specifically this code here:

https://github.com/apache/arrow-rs/blob/c561acba798d34f7e642eca44b298c2a3b63ff98/parquet-variant-compute/src/variant_array.rs#L341-L340

Describe alternatives you've considered

Ideally we would find a way to reuse the macros being developed for cast_to_variant kernel as suggested by @Samyak2 above.

Additional context

[klion26]

I'm trying to support this by enhancing the existing macro like below

• add one more rule for the VariantArray::value
• change the existing rule(add builder => in the existing rule)

#[macro_export]
macro_rules! cast_conversion {
    ($t:ty, $method:ident, $cast_fn:expr, $input:expr, builder => $builder:expr) => {{
        let array = $input.$method::<$t>();
        for i in 0..array.len() {
            if array.is_null(i) {
                $builder.append_null();
                continue;
            }
            let cast_value = $cast_fn(array.value(i));
            $builder.append_variant(Variant::from(cast_value));
        }
    }};
    ($t:ty, $method:ident, $cast_fn:expr, $input:expr, index => $index:expr) => {{
        let array = $input.$method::<$t>();
        let cast_value = $cast_fn(array.value($index));
        Variant::from(cast_value)
    }};
}