fix: native rounded keyboard detection

[kirillzyusko]

📜 Description

Added keyboardBorderRadius variable as exported constant from this module.

💡 Motivation and Context

On iOS 26 keyboard started to have a rounded corners. However, if you compile app with XCode 26 or if you intentionally disable new keyboard via plist file you will get old keyboard. At the moment KeyboardToolbar relies on iOS 26 presence only and it may cause inconsistencies.

In this PR I'm fixing it by adding an exported constant that indicates a radius of keyboard. Now we can compare it with 0 to understand which exactly keyboard is shown.

These changes will also need to be present to make #1409 working across all devices 🤞

📢 Changelog

JS

• declared getConstants method on native module;
• updated TS spec and included new method signature;
• declared KEYBOARD_BORDER_RADIUS in constants file;
• used KEYBOARD_BORDER_RADIUS in KeyboardToolbar code.

iOS

• added usesModernKeyboard helper;
• added constantsToExport/getConstants module method;

Android

• added keyboardBorderRadius variable as exported constant;
• added getConstants method to module;

🤔 How Has This Been Tested?

Tested manually fabric/paper on iPhone 15 (iOS 15.5)/iPhone 17 Pro (iOS 26.2)/Pixel 9 Pro (API 35).

📸 Screenshots (if appropriate):

📝 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
309906 bytes	309372 bytes	534 bytes 📈