Support auto-completion for TSDoc

Nobody has claimed this yet.

### 🔍 Search Terms

tsdoc complete

### ✅ Viability Checklist

- [x] This wouldn't be a breaking change in existing TypeScript/JavaScript code
- [x] This wouldn't change the runtime behavior of existing JavaScript code
- [x] This could be implemented without emitting different JS based on the types of the expressions
- [x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
- [x] This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
- [x] This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

### ⭐ Suggestion

TypeScript currently only supports auto-completion for JSDoc, not TSDoc. For example, there is no intelligent suggestion for [@defaultValue](https://tsdoc.org/pages/tags/defaultvalue/).


### 📃 Motivating Example

If [TSDoc](https://tsdoc.org/) is the recommended commenting standard for TypeScript, then it should natively support intelligent suggestions and syntax highlighting for TSDoc.

### 💻 Use Cases

Writing comments using TSDoc syntax in VSCode.

Start by investigating how TypeScript currently provides JSDoc auto-completion and how VSCode consumes those language-service results. Compare that behavior with TSDoc tags such as @defaultValue and determine the expected syntax-highlighting and completion behavior; done means TSDoc comments receive intelligent suggestions without changing emitted JavaScript.

Written by the indexing model from the issue text.