[5.14.5] TextInput with multiline inside Portal causes rapid flicker and infinite onChangeText calls [iOS]

### Current behaviour
Typing in a `react-native-paper` `TextInput` with `multiline` **inside a `Portal`** causes rapid flicker and floods `onChangeText` (dozens of calls per second). Removing **either** `Portal` or `multiline` stops the issue.

### Expected behaviour
No flicker; `onChangeText` fires once per user input.

### How to reproduce?
1. Render a multiline `TextInput` inside a `Portal`.
2. Run iOS
3. Focus the field and type characters.

```tsx
import * as React from 'react';
import { Portal, TextInput } from 'react-native-paper';

export default function Repro() {
const [text, setText] = React.useState('');
return (

{
console.count('onChangeText'); // spams rapidly
setText(t);
}}
style={{ minHeight: 120 }}
/>

);
}
```

### What have you tried so far?
- Removing `multiline` → issue gone
- Removing `Portal` → issue gone

### Your Environment

| software | version |
|------------------------|----------|
| ios | x |
| android | x |
| react-native | **0.81.5** |
| react-native-paper | **5.14.5** |
| node | x.x.x |
| npm or yarn | x.x.x |
| expo sdk | N/A |

Start by reproducing the issue on iOS with the provided Portal and multiline TextInput example, then inspect the Portal and TextInput entry points. Done means typing no longer causes flicker and onChangeText fires once per user input.

索引モデルが issue の本文から書いたものです。