fix: KeyboardExtender initial mount on Fabric (#1135)

## 📜 Description

Fixed initial display of `KeyboardExtender` on Fabric (potentially iOS
26 specific only).

## 💡 Motivation and Context

When view is initially mounted, then `oldProps.enabled` and
`newProps.enabled` will be `true`, so we'll never update `_enabled` (the
only one case is to set it to `false` and then back to `true` on JS).
This fix is similar to
#1040
- we don't need to rely on old props and instead we need to compare with
our own internal state.

Closes
#1133

## 📢 Changelog

<!-- High level overview of important changes -->
<!-- For example: fixed status bar manipulation; added new types
declarations; -->
<!-- If your changes don't affect one of platform/language below - then
remove this platform/language -->

### iOS

- change `if (newViewProps.enabled != oldViewProps.enabled) {` to `if
(newViewProps.enabled != self.enabled) {`

## 🤔 How Has This Been Tested?

Tested on iPhone 16 Pro (iOS 26).

## 📸 Screenshots (if appropriate):

|Before|After|
|-------|-----|
|<img width="1206" height="2622" alt="image"
src="https://github.com/user-attachments/assets/f0167f56-d069-4d27-8a44-b4cdb061a01b"
/>|<img width="1206" height="2622" alt="image"
src="https://github.com/user-attachments/assets/fa290038-7d5e-45f4-8c95-81ac6d75d313"
/>|

## 📝 Checklist

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

Author: kirillzyusko

ios/views/KeyboardExtenderManager.mm

@@ -222,10 +222,9 @@ - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
 #ifdef RCT_NEW_ARCH_ENABLED
 - (void)updateProps:(Props::Shared const &)props oldProps:(Props::Shared const &)oldProps
 {
-  const auto &oldViewProps = *std::static_pointer_cast<const KeyboardExtenderProps>(_props);
   const auto &newViewProps = *std::static_pointer_cast<const KeyboardExtenderProps>(props);
 
-  if (newViewProps.enabled != oldViewProps.enabled) {
+  if (newViewProps.enabled != self.enabled) {
     [self updateEnabledState:newViewProps.enabled];
   }