Add support for `@file` jsdoc tag to describe a module

### 🔍 Search Terms

`fileoverview`

### ✅ 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

JSDoc supports the [`@file`](https://jsdoc.app/tags-file) tag to document a file (module). Synonyms are `@fileoverview` and `@overview`.

Currently TypeScript allows you to document a module like this:

```ts
/**
* This comment describes `some-module`.
*/
declare module 'some-module' {
/**
* This comment describes `fn`.
*/
export function fn(): unknown;
}
```

This description shows up when you hover over an import of `some-module`.

However, it’s generally considered more idiomatic avoid `declare module`:

```ts
/**
* This comment describes `fn`.
*/
export function fn(): unknown;
```

In this case, there’s not way to describe the module.

I believe the `@file` tag provides a perfect way to describe a module. So the following code would be equivalent to the original example above.

```ts
/**
* @file
* This comment describes `some-module`.
*/

/**
* This comment describes `fn`.
*/
export function fn(): unknown;
```

I noticed that current module descriptions show up on hover, but not in autocomplete. I believe it would be nice to add support for that too.

### 📃 Motivating Example

TypeScript now supports the [`@file`](https://jsdoc.app/tags-file) tag to describe a module.

### 💻 Use Cases

1. What do you want to use this for?

I would describe modules. It would be nice to generate documentation from source as well.

2. What shortcomings exist with current approaches?

It can’t be done without `declare module`.

3. What workarounds are you using in the meantime?

I don’t document modules.

Start by tracing how existing module descriptions are collected and surfaced in hover, then inspect the JSDoc processing and autocomplete paths. Determine how the @file, @fileoverview, and @overview tags should identify a module without declare module. Done means module descriptions work for the shown export pattern and appear consistently in hover and autocomplete.

Written by the indexing model from the issue text.