Type variables in type abstractions are not properly concretized

@weswigham đang làm issue này rồi.

Từ ngày 24/1/2025.

### 🔎 Search Terms

type variables unknown

### 🕗 Version & Regression Information

- This changed between versions 4.9.5 and 5.0.4.

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.3#code/MYewdgzgLgBAZjAvDAPADQDQD4AUBzALlQEFscAjItASiSxkxgitsXrxwmoG4AoX0JFgAnAKaxkcHCgBCZAB5EZregEYMMAETRhmnrwD0BmCZgA9APxA

### 💻 Code

```ts
const f = (g: (b: X) => X, s: X) => g(s);

const ret = f((x: B) => 1, "str");
// ^? const ret: unknown
```

### 🙁 Actual behavior

No type error is reported and `ret` is inferred as `unknown` type.

### 🙂 Expected behavior

I think a type error is reported because the call to `f` attempts to concretize the type variable X not only as a number but also as a string. In fact, TypeScript 4.9.5 reported a type error.

### Additional information about the issue

I am not sure that TypeScript 4.9.5 was perfect. The following code is inferred to be `unknown`, but I think `string` is correct. This behavior was back to TypeScript 3.5.1.

```ts
const f = (g: (b: X) => X, s: X) => g(s);

const ret = f((x: B) => x, "str");
// ^? const ret: unknown

// actual: ret is inferred as unknown
// expected: ret is inferred as string
```
https://www.typescriptlang.org/play/?ts=5.7.3#code/MYewdgzgLgBAZjAvDAPADQDQD4AUBzALlQEFscAjItASiSxkxgitsXrxwmoG4AoX0JFgAnAKaxkcHCgBCZAB5EZrevIwwARNGEaevAPT6YxmAD0A-P0MwAhsCgBXGwBsiY2AEsIMD2DijhMQATW28HMABrMBAAdzADI1F5AAdRe1Egt3Efb19-QIzQpihhXzwgA

I also found a strange behavior that a type variable that should have been concretized was returned without being concretized. I thought this is related, but I could be wrong. Sorry if so.

```ts
const f = (g: (x: X) => X) => g;

const h = f((x: number) => 1);
// ^? const h: (x: X) => X

h(1);
// actual: type error
// expected: no type error
```
https://www.typescriptlang.org/play/?ts=5.7.3#code/MYewdgzgLgBAZjAvDAPADQDQD4AUBzALlQEFscAPItASiSxhrpjxWgCcBLMPLAbgCh+oSLAAWSeCjABXALYAjAKZtcKAEJlKMGQuW1E9AIzUBAelMxLMAHoB+QaJzGzFgIbAo01wBsiUAJ4ADoowymwgbPzmoeTBHooAJkRgIDABwaFs4WxAA