fix(ios): avoid incorrectly updating caret position

[ouchuan]

Avoid incorrectly updating caret position

Summary:

Pull Request resolved: #50641

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

Changelog:

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

Test Plan

Tested with the following code(a simplified version from the code in #50641)

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.

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[ouchuan]

@cipolleschi hello, This PR is trying to fix #50680, can you take a look?

[cipolleschi]

@ouchuan thanks for the fix. The code makes sense to me.

[facebook-github-bot]

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@cipolleschi merged this pull request in 7771317.

[react-native-bot]

This pull request was successfully merged by @ouchuan in 7771317

^{When will my fix make it into a release? | How to file a pick request?}

[react-native-bot]

This pull request was successfully merged by @ouchuan in 89f4dd2

^{When will my fix make it into a release? | How to file a pick request?}