Broken inference for generic classes passed to a generic function taking an optional class

@ahejlsberg y travaille déjà.

Depuis le 30/4/2025.

### 🔎 Search Terms

class inference, optional class, broken inference

### 🕗 Version & Regression Information

This changed in PR https://github.com/microsoft/TypeScript/pull/31116

However, this was the first time that there was even a distinction between a generic and non-generic class during inference to my knowledge. This likely means this has existed ever since the ability to infer a generic class has existed.

### ⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAggdiAwgezgZ2AJwK4GNjKZQC8UcEA7lABQB09AhpgOZoBcUDCA2gLoCUJAHxRkAIwBWEfAG4AUHIBm2OPgCWqKACUIcACYRMAMQA2DVgFk1ADzVwAPACEGaCIjNo0UCNeC69XvBIqBg4+IRQAD5QKgaKdhB6JDH6EPHkekLUclC5UM6uAPwcBW4eaAA0coIA3gC+8nK45VAocMAMCZj2ACoi9Qo6qcZmljZ21G0dXfxyAPRzeUvLeQB6sCzYALa6wKKKUKCQUADkRxDIB1Od5JgnUGpecMh7LmhqzHAMYibQBFBgJgMHZ+IiXQ7gaAnWJpBJ6E60IA

### 💻 Code

```ts
type AnyConstructor = new (...args: any[]) => object;

function RenderFlagsMixin(
Base?: BaseClass,
) {};

class Container {}
// ^ Only happens when the class is generic.

RenderFlagsMixin(Container)
// ^ Argument of type 'typeof Container' is not assignable to parameter of type 'undefined'.
```

### 🙁 Actual behavior

`BaseClass` is inferred as `undefined` despite the call being the value `Container`.

### 🙂 Expected behavior

`BaseClass` should be inferred as `typeof Container`.

### Additional information about the issue

_No response_