Add toposort to ensure outputs are printed in valid order

[sdboyer]

Currently, cuetsy prints its outputs in alphabetical order. TS is sensitive to ordering in its constant declarations, however, meaning that this:

interface Bar {
  N: number;
}

const defaultBar: Bar = {
  N: defaultFoo,
}

type Foo = number;
const defaultFoo: Foo = 4;

Is invalid because defaultFoo is declared after it is referenced in defaultBar. Consequently, we have to add a (stable) toposort to cuetsy such that its const outputs are in an acceptable order.

It'll also mean erroring on circular references, if any.

[frossano-grafana]

we can re-discuss this later because if things are declared in order in the CUE file then it's not an issue