RegExp.prototype[Symbol.matchAll] doesn't respect `v` flag

[Sosuke Suzuki]

poc:

```js
function doMatchAll(regex) {
    const text = '𠮷a𠮷';
    const matches = [...RegExp.prototype[Symbol.matchAll].call(regex, text)];
    print(matches.map(match => match.index));
}

doMatchAll(/(?:)/g);
// expected: 0,1,2,3,4,5
// actual  : 0,1,2,3,4,5

doMatchAll(/(?:)/gu); // 0,2,3,5
// expected: 0,2,3,5
// actual  : 0,2,3,5

doMatchAll(/(?:)/gv); // 0,1,2,3,4,5
// expected: 0,2,3,5
// actual  : 0,1,2,3,4,5
```

[Sosuke Suzuki]

Pull request: https://github.com/WebKit/WebKit/pull/26933

[EWS]

Committed 277160@main (4b84428a9535): <https://commits.webkit.org/277160@main>

Reviewed commits have been landed. Closing PR #26933 and removing active labels.

[Radar WebKit Bug Importer]

<rdar://problem/126017731>