Round trips through `ScalarValue`'s sometimes don't preserve types (e.g. change types from `DictionaryArray`)

[alamb]

Describe the bug

Various parts of the DataFusion codebase assume that the transformation between ScalarValue <--> Array have the same datatype. This would seem to be a reasonable assumption, however it does not hold for at least for DictionaryArrays

For example, a ScalarVaule that is converted to an array, casted to a DictionaryArray<_> due to coertion rules, and then converted back to a ScalarVaule. When that supposedly cast ScalarValue is converted back to an Array, it does not maintain its Dictionary encoding, instead it results in a DataType::Utf8

To Reproduce

fn bad_cast() {
    // here is a problem with round trip casting to/from a dictionary
    // array. It is desired to cast this ScalarValue to a Dictionary
    // (for coertion, for example)
    let scalar = ScalarValue::Utf8(Some("foo".to_string()));

    let desired_type = DataType::Dictionary(
        // key type
        Box::new(DataType::Int32),
        // value type
        Box::new(DataType::Utf8)
    );

    // convert from scalar --> Array to call cast
    let scalar_array = scalar.to_array();
    // cast the actual value
    let cast_array = kernels::cast::cast(&scalar_array, &desired_type).unwrap();
    // turn it back to a scalar
    let cast_scalar = ScalarValue::try_from_array(&cast_array, 0).unwrap();

    // Some time later the "cast" scalar is turned back into an array:
    let array = cast_scalar.to_array_of_size(10);

    // The datatype should be "Dictionary" but is actually Utf8!!!
    assert_eq!(array.data_type(), &desired_type)
}

Running this function results in

  left: `Utf8`,
 right: `Dictionary(Int32, Utf8)`', src/main.rs:80:5

Expected behavior
Test case should pass

Additional context
I am not sure if it makes sense to add a ScalarValue::Dictionary type variant, or perhaps add a is_dictionary flag or something else, or maybe even just not assume a ScalarValue can be round tripped and maintain its data type

This is the root cause of #2873 -- I added a patch for that particular case but this problem can occur elsewhere

[alamb]

This is not dissimilar to the issue @comphead is working on in #2840