fix(ios): block screen touches while header UIMenu is open

[jasleenkaur-qed42]

Summary

• Block RN screen content from receiving touches while a native stack header UIMenu is open
• Restore interaction when the menu is dismissed (outside tap) or a menu item is selected
• Fixes [iOS] Header menu should block presses from reaching screen content #4139

Problem

On iOS, when using unstable_headerRightItems with type: 'menu', taps on screen content (e.g. Pressable) still fired while the menu was open. Native apps block those touches.

Solution

• RNSBarButtonItem: wrap menu children in UIDeferredMenuElement and invoke a menuPresented callback before the menu appears (dispatched on main queue)
• RNSScreenStackHeaderConfig: wire callback to RNSScreenStackView
• RNSScreenStack: while menu is open, disable top screen content interaction and install a one-shot gesture recognizer to intercept outside-dismiss taps before Fabric's touch handler

Test plan

• Run repro: https://github.com/ferrannp/menu-header-screens (or local rn-screens-menu-repro)
• Open header menu (⋯)
• While menu is open, tap Increment counter → should not increment
• Dismiss menu by tapping outside → tap Increment counter → should increment
• Dismiss menu by selecting an item → screen touches work again
• Verify left header button and back navigation still work