fix: use weak reference to keyboard view on iOS (#1465)

## 📜 Description

Use `weak` reference to `KeyboardView`.

## 💡 Motivation and Context

The keyboard is a system view and we don't manage a lifecycle of this
view. So we shouldn't try to keep a reference to it when view has been
destroyed. For that we need to use `weak` keyword so that when keyboard
instance has been destroyed we'll try to find a new instance of the
keyboard.

## 📢 Changelog

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declarations; -->
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### iOS

- use `weak` reference to the keyboard view in `KeyboardViewLocator`;

## 🤔 How Has This Been Tested?

Tested via e2e tests. The issue has been discovered on iOS 26.2 (there
after keyboard dismissal the reference is stale and keyboard is getting
re-created when it's getting shown again).

## 📝 Checklist

- [x] CI successfully passed
- [x] I added new mocks and corresponding unit-tests if library API was
changed