[iOS] Fix ScrollView stale keyboard inset after dismiss

[Miyou]

Summary:

This fixes an iOS ScrollView bug where using automaticallyAdjustKeyboardInsets together with contentInsetAdjustmentBehavior="automatic" can leave a stale bottom gap after the keyboard is dismissed. The extra space is not cleared until the user scrolls again.

The underlying issue is that the keyboard dismissal path can call scrollToOffset with an offset that needs to be clamped against the new inset-adjusted bounds, but the current code checks for an unchanged contentOffset before that clamping happens. When adjustedContentInset shrinks after the keyboard closes, the numeric offset can compare equal while still being outside the valid range, so setContentOffset is skipped and the stale gap remains visible.

This change:

• clamps the target offset before the equality check
• uses the effective inset (adjustedContentInset when available) when computing the valid scroll range
• applies the same behavior to both Paper and Fabric iOS scroll view implementations
• adds an RNTester repro for the automaticallyAdjustKeyboardInsets + contentInsetAdjustmentBehavior="automatic" combination

Changelog:

[IOS] [FIXED] Fix ScrollView leaving stale bottom inset after keyboard dismissal when using automaticallyAdjustKeyboardInsets with automatic content inset adjustment

Test Plan:

1. Reproduced the issue in a minimal Expo app on iOS with:
   • automaticallyAdjustKeyboardInsets
   • contentInsetAdjustmentBehavior="automatic"
   • a TextInput near the bottom of the scroll view
2. Built the app with React Native compiled from source so the native iOS changes were used.
3. Verified on the iOS simulator that:
   • focusing the text input moves content above the keyboard
   • dismissing the keyboard returns the content to the original position
   • no extra bottom gap remains and no manual scroll is required to reset layout
4. Added a dedicated RNTester scenario in ScrollViewKeyboardInsetsIOSExample.js that reproduces this exact prop combination for upstream verification.

Build/validation details:

• npx expo prebuild --platform ios --no-install
• npx pod-install ios
• xcodebuild -workspace ios/scrollviewautomaticallyadjustkeyboardinsetsbug.xcworkspace -scheme scrollviewautomaticallyadjustkeyboardinsetsbug -configuration Release -sdk iphonesimulator -destination 'platform=iOS Simulator,name=iPhone 16 Pro' build

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Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Meta Open Source project. Thanks!