[Variant] Implement `cast_to_variant` kernel

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
As @Samyak2 noted on https://github.com/apache/arrow-rs/pull/8021/files#r2249926579, having the ability to convert FROM a typed value to a VariantArray will be important

For example, in SQL it could be used to cast columns to variant like in some_column::variant

Describe the solution you'd like

I would like a kernel like this:

/// Casts a typed arrow [`Array`] to a [`VariantArray`]. This is useful when you
/// need to convert a specific data type
pub fn cast_to_variant(input: &dyn Array) -> Result<VariantArray, ArrowError> {

Describe alternatives you've considered

I started down a templated route (see below) that got somewhat complicated

Additional context

[alamb]

label_issue.py automatically added labels {'parquet'} from #8044