Conditional type flow types missing in the template in mapped types with as clause

Nadie ha tomado este issue todavía.

### 🔎 Search Terms

as clause renaming filtering mapped type conditional type flow

### 🕗 Version & Regression Information

- This is the behavior in every version I tried

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.0-dev.20250222#code/C4TwDgpgBAggxnCZgDkD2A7FBXANrgQwCNcIAeAFSggA9gIMATAZygG8BfAPigF4oKAbgBQw0JAERmwSj35thUKAG0A0lACWGKAGsIINADMBUAqwpqAutToMW7DlAD8UdQC4oGCADcIAJ0sPeERkdCw8QhJyC1VLLhEOESA

### 💻 Code

```ts
type AcceptNonNullable = T;

type Test = {
[K in keyof T as T[K] extends {} ? K : never]: AcceptNonNullable;
};
```

### 🙁 Actual behavior

`AcceptNonNullable` errors with:
```
Type 'T[K]' does not satisfy the constraint '{}'.
Type 'T[keyof T]' is not assignable to type '{}'.
Type 'T[string] | T[number] | T[symbol]' is not assignable to type '{}'.
Type 'T[string]' is not assignable to type '{}'.(2344)
```

### 🙂 Expected behavior

It doesn't have to error. It's known that `T[K]` has to extend `{}` at this position

### Additional information about the issue

_No response_

Comienza con la reproducción enlazada de TypeScript Playground e inspecciona cómo el comprobador de tipos gestiona la cláusula `as` y la restricción condicional del tipo mapeado. Rastrea por qué no se reconoce la restricción de `AcceptNonNullable` y confirma después que el ejemplo ya no informa del error 2344, conservando el comportamiento de filtrado.

Escrito por el modelo de indexación a partir del texto del issue.