fix: KeyboardExtender width on iPad in split mode

[kirillzyusko]

📜 Description

Use window size instead of screen.

💡 Motivation and Context

Originally I added code in #948 (used subscription on screen instead of window). In #957 I realized that new approach has downsides and started to use layoutSubviews method instead of subscription to events that apple provides (and I kept using screen size as main source of truth). However on iPad in multi-task/stage-manager mode screen size may not reflect a real window size (because if window is floating it can be much smaller than the screen).

So in this PR I'm refining solutions made in #948 and #957. We still need to use window as main source of truth and we need to read it in layoutSubviews because new dimensions may not be available in events that we receive from notification center.

I tested repo provided in #948 and #957 and with new code they still seem to work well:

948	957
Simulator.Screen.Recording.-.iPhone.16.Pro.-.2025-09-08.at.17.24.03.mp4	Simulator.Screen.Recording.-.iPad.Pro.11-inch.M4.16GB.-.2025-09-08.at.17.27.25.mp4

Closes #1045

📢 Changelog

JS

• read window dimensions instead of screen;

iOS

• use self.window instead of UIScreen.main;

🤔 How Has This Been Tested?

Tested manually on iPad 11 Pro (m4, 16GB, iOS 18.5).

📸 Screenshots (if appropriate):

Before	After

📝 Checklist

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

[github-actions]

📊 Package size report

Current size	Target Size	Difference
212978 bytes	212955 bytes	23 bytes 📈