Parameters in functions with type parameters are not contextually-typed

@ahejlsberg がすでに取り組んでいます。

2025年6月4日 から。

### 🔎 Search Terms

type parameters generic conextual parameter types context sensitive

### 🕗 Version & Regression Information

- This is the behavior in every version I tried

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.0-dev.20250601#code/KYDwDg9gTgLgBAE2AYwDYEMrDsiA7AZ3gDM8AuOAHgBUAaOAQSgHMC5QZg8E2mp0AnpXR4BAPnoAlYDDEAKALAAoOHALBUxCnWWqARhAQCKcmAAsAlgW30AdPcysKTVgEo4AXjFwA4l2D8MNDColIy9HjAAG4BYsruXnBy9raO1owsBAne0jDKyqCQsDj4RHAQANaecKRyAN5wALbABATozMAUAETEEBBdcAC+9MQArnjIMBb4AFRy5HB4o416Ae51uiWEEKjAtqgQzKaWBLbNre3AEa7KgzdKBeDQ8LiE8HgQ1bUN520d3b1+kMRuNJtM8DNKAA5eQLKHrTavAg7PYHI7mKxnFp-K6Le53ZRAA

### 💻 Code

```ts
export declare const fn: , Ret>(
self: T,
body: (this: T, ...args: Args) => Generator
) => (...args: Args) => Ret

export const ok = fn({ message: "foo" }, function*(n: number) {
console.log(this.message, n) // ok
})

export const no = fn({ message: "foo" }, function*(n: N) {
console.log(this.message, n) // error
})
```

### 🙁 Actual behavior

The second case errors

### 🙂 Expected behavior

Both of those should work fine

### Additional information about the issue

Given TS is able (at times) to infer new generic signatures based on generic function arguments (notice the return type of the failing case: `const no: (n: N) => void`), it makes sense to assign contextual parameter types.