abstract type guard does not narrow when keyed with a unique symbol

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### 🔎 Search Terms

abstract type guard symbol

### 🕗 Version & Regression Information

- This is the behavior in every version I tried, and I reviewed the FAQ for entries about abstract type guard

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250810&ssl=28&ssc=2&pln=1&pc=1#code/FAYw9gdgzgLgBASygIQIYCc4F44GUCeAtgEZgA2AFAERJrpUCUA3MMKsbOqiPCGalChwAYmDBwA3sDgy47Tt3i0MFBgC44MABZJEQui1lyOMLjzgBtZegC6qjdt26DrI4QCm2sABN7cAG5gCN6S0kayCABmcBSOUFYoGHYMDKHh6XAA9JlwACo6QlBaYACuZCEQYPDE7nIQcO7o6GDoYRmycQB0xBgAsp7Fvsxt4QC+DWRQtVExXdaqqVLtRl096P1eQ4YZoyO7u6D8gnB0DQAeMO4Q3kKi4kuyYP6N6MHTieh+cXonGGkZ6E8JXQ9VMJXc2xkByMTxeb0s1mSDgKP1OD3SgJgwNB6HBkLg0Nkaw2gz8gWCkn2QA

### 💻 Code

```ts
const isBar = Symbol("isBar");

abstract class Foo {
abstract isBar(): this is Bar;
abstract [isBar](): this is Bar;

method(): void {
if (this[isBar]()) {
// This should not be an error, it should work the same as .isBar()
this.barMethod();
} else if (this.isBar()) {
this.barMethod();
}
}
}

class Bar extends Foo {
override isBar(): this is Bar {
return true;
}

override [isBar](): this is Bar {
return true;
}

barMethod(): void {}
}
```

### 🙁 Actual behavior

TS reports an error:

> `Property 'barMethod' does not exist on type 'Foo'. Did you mean 'method'?(2551)`

### 🙂 Expected behavior

No error should happen here, the type guard should work the same as the non-symbol version of the method.

### Additional information about the issue

_No response_

Inizia con il TypeScript Playground collegato e riproduci la differenza tra la chiamata unique-symbol e la chiamata denominata isBar() in Foo.method(). Traccia il comportamento del restringimento dei tipi per entrambe le guardie di tipo astratte, quindi verifica che la chiamata basata su una chiave simbolica restringa this a Bar e non segnali più l’errore barMethod.

Scritto dal modello di indicizzazione a partire dal testo della issue.