Allow getAccessibilityTree to be case-insensitive

We could make it ignore case changes by always lowercasing the output

```ts
await getAccessibilityTree(
el,
{
caseInsensitive: true
}
)
```

I am not sure yet if this is a useful enough feature since it depends on how often the case of the text changes without the text itself changing. If that happens often, this could be useful, but otherwise, I'm not sure this feature is worth it.