Custom JSDoc type cannot be extended

@sandersn arbeitet bereits daran.

Seit 09.7.2025.

Does this issue occur when all extensions are disabled?: Yes/No

- VS Code Version: 1.99.3
- OS Version: Linux x64 6.11.0-24-generic

Steps to Reproduce:

1. Define a base JSDoc type:
```js
/**
* @typedef {object} baseType
* @property {string} baseProperty
*/
```
2. Define a child type and add a property:
```js
/**
* @typedef {baseType} childType
* @property {string} childProperty
*/
```

Expected behavior: `childType` has `baseProperty` from `baseType` and `childProperty` from the own definition.

Actual behavior: `childType` has only `baseProperty` from `baseType`.

However, it works in WebStorm: