[iOS] Avoid unnecessary string allocations

[m-bert]

Description

#3290 introduced recursive algorithm to obtain accessibility label from children. However, unlike in React Native, it allocates String at every recursive call. This may lower the performance as those allocations come at high cost.

Test plan

Accessibility labels are inferred as before.

[hirbod]

And what about the infinite recursion? It’s extremely hard to repro, but it can happen. In our case, it was happening randomly when I touched a RectButton inside our LegendList. Sometimes, just backgrounding and foregrounding the app (and likely re-rendering the RectButton in the list) would trigger it. After about 60 seconds of hanging, memory would spike from 300MB to 7GB and the app would crash. It’s hard to tell when and how this happens, but it feels like some kind of bailout mechanism (max depth check) is missing, no? For sure just a bandaid and not the root issue, at least if would prevent those crashes

[m-bert]

And what about the infinite recursion?

We'd like to take a closer look into this issue. Sure, setting max depth is a solution, but maybe we will be able to figure out how to fix it in a better way. Given that, we will do this in another PR. Also it would be great if you could provide a reproduction (if possible).

If you need these changes asap, you can make a patch which reverts this commit. This is where these changes were introduced, so reverting it should make it work again.

[hirbod]

I fixed the recursion issue for now by just providing an accessibilityLabel to every RectButton, so I’m good and don't need a patch. But I saw a few people on X saying they ran into the same issue, so it might affect more people.

I'll try my best to come up with a repro but this is a tough one for sure.

[hirbod]

FYI, the issue is reproducible with Pressable by react-native as well. So this is a core issue!