Go-to-type definition does not work on aliases to tuple types

```ts
export type SpanMapping = [
virtualStart: number,
virtualLength: number,
originalStart: number,
originalLength: number,
kind: SpanMapKind,
features?: SpanMapFeature,
];
export let mapping: SpanMapping;
mapping/**/;
```

If you request *go to type definition* at `/**/`, you will get no result.

The same is not true if `SpanMapping` is aliased to an anonymous object type.

Start by reproducing the provided TypeScript example and request go-to-type-definition at the marked position. Compare the result for the tuple alias with the anonymous object alias. Done means the tuple alias returns a type-definition result like the object alias.

Written by the indexing model from the issue text.