Support try_from_array and eq_array for ScalarValue::Union

[joroKr21]

Which issue does this PR close?

Part of #2326

Rationale for this change

Extending support for union types to primitive operations.

What changes are included in this PR?

Added support for DataType::Union to ScalarValue::try_from_array and ScalarValue::eq_array.

Are these changes tested?

Added unit tests (we don't have slt tests yet, see #10161)

Are there any user-facing changes?

Not directly, but more functions will work on union types.