Implement transform_literal for TransformFunction

[ZENOTME]

I'm quite unsure about the fn transform and the handling of the arrow_array - seems kinda clunky?

I think the transform can provide an interface like transform_literal later.

pub trait TransformFunction: Send {
    /// transform will take an input array and transform it into a new array.
    /// The implementation of this function will need to check and downcast the input to specific
    /// type.
    fn transform(&self, input: ArrayRef) -> Result<ArrayRef>;
+ fn transform_literal(&self, literal:Literal) -> Result<Literal>; 
}

Originally posted by @ZENOTME in #269 (comment)