Use a consistent ordering when writing union types

In DefinitelyTyped, `$ExpectType` assertions depend on a type having a consistent string represenation across TypeScript versions. It looks like the ordering of union types is dependent on some implementation details that change between versions. When we output unions as strings, we should sort them in some consistent way first instead of just using whatever order we happened to use internally. I would suggest this ordering: * numeric literals, low to high * string literals, low to high (by `<`) * named types (including type aliases, enum, class and interface names), by name * function literals: by length (`() => void` before `(x: number) => void`), then by parameter name, then by parameter type * type literals: Sorted smallest to largest (`{ x: number }` before `{ x: number, y: number }`); and type literals of the same size should be alphabetically sorted by property (`{ a: number }`) before `{ b: number }`) or by the sorting of values (`{ s: "a" }` before `{ s: "b" }`) Of course, another solution would be to try to handle this in `$ExpectType` by parsing out unions and allowing it if any sorting is valid. But it is strange in TS to see a string literal union displayed in a seemingly random order.