fix(ios): avoid incorrectly updating caret position (#50680)

Summary:
Avoid incorrectly updating caret position

Pull Request resolved: https://github.com/facebook/react-native/issues/50641

The caret position is updated incorrectly when a user is first typing if an zero-length selection is set.

[IOS] [CHANGED] - Typing into TextInput now will not cause the caret position to update to the beginning when a zero-length selection is set.

Pull Request resolved: https://github.com/facebook/react-native/pull/50680

Test Plan:
Tested with the following code(a simplified version from the code in https://github.com/facebook/react-native/issues/50641)
```js
const [selection, setSelection] = useState({start: -1, end: -1});
const onSelectionChange = (
      evt: NativeSyntheticEvent<TextInputSelectionChangeEventData>,
    ) => {
      const {selection} = evt.nativeEvent;
      const {start, end} = selection;
      console.log('selection change: ', start, end);
      setSelection(selection);
};
return (
  <View style={{ position: 'absolute', top: 50, left: 30 }}>
    <TextInput
      placeholder="test"
      selection={selection}
      onSelectionChange={onSelectionChange}
    />
  </View>
);
```
When using the main branch, the caret position will jump back to the beginning after the first typing.
It works fine after applying this commit.

Reviewed By: fabriziocucci

Differential Revision: D72957245

Pulled By: cipolleschi

fbshipit-source-id: 3586797332b35e86b17f386a35e7d192ff758f7e