Add support for single line enum formatting

[kayagokalp]

Currently, enums are always formatted into multiple lines but I guess we should do the same thing we are doing for structs and storage (once #2124 is merged) which is deciding whether to format into single or multiple lines based on the length.

So once we address this issue we should be able to format:

enum Color {
    Blue: (),
    Green: (),
}

to something like:

enum Color { Blue: (), Green: () }