clientgen/typescript: Add parentheses when lists element type is union

[fredr]

Fixes wrapping list of unions with parentheses

interface Response {
  message: string;
  item?: Item;
}

interface X {
  a: string;
}
interface Y {
  b: (keyof X)[];
}

type Thing = { a: string; b: number };
type Item = {
  keys: (keyof Thing)[];
  otherField: ((X & Y) | X | Y)[];
};

Now generates the following type:

export interface Item {
    keys: ("a" | "b")[]
    otherField: ({
        a: string
        b: "a"[]
    } | X | Y)[]
}

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