Function variant_get 

pub fn variant_get(
    input: &ArrayRef,
    options: GetOptions<'_>,
) -> Result<ArrayRef>

Returns an array with the specified path extracted from the variant values.

The return array type depends on the as_type field of the options parameter

1. as_type: None: a VariantArray is returned. The values in this new VariantArray will point to the specified path.
2. as_type: Some(<specific field>): an array of the specified type is returned.

TODO: How would a caller request a struct or list type where the fields/elements can be any variant? Caller can pass None as the requested type to fetch a specific path, but it would quickly become annoying (and inefficient) to call variant_get for each leaf value in a struct or list and then try to assemble the results.