fix: KeyboardAvoidingView height when "Prefer Cross-Fade Transitions" is enabled

[gabrieldonadel]

Summary

Fix KeyboardAvoidingView height on iOS when "Prefer Cross-Fade Transitions" is enabled by adding an additional check to _relativeKeyboardHeight verifying if prefersCrossFadeTransitions() is true and keyboardFrame.screenY is 0 and treating this special case. The issue was caused by the native RCTKeyboardObserver where the endFrame reported by UIKeyboardWillChangeFrameNotification returns height = 0 when Prefer Cross-Fade Transitions" is enabled and unfortunelly there isn't much we can do on the native side to fix it.

Closes https://github.com/facebook/react-native/issues/31484 Closes https://github.com/facebook/react-native/issues/29974

Changelog

[iOS] [Fixed] - Fix KeyboardAvoidingView height when "Prefer Cross-Fade Transitions" is enabled

Test Plan

On iOS 14+

1. Access Settings > "General" > "Accessibility" > "Reduce Motion", enable "Reduce Motion" then enable "Prefer Cross-Fade Transitions".
2. Open the RNTester app and navigate to the KeyboardAvoidingView page
3. Focus and blur inputs and observe the keyboard behaving correctly

https://user-images.githubusercontent.com/11707729/186822671-801872be-7db1-4c5c-904b-1987441c1326.mov

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	7,618,232	-16,250
android	hermes	armeabi-v7a	7,032,488	-13,914
android	hermes	x86	7,918,294	-18,019
android	hermes	x86_64	7,891,912	-16,263
android	jsc	arm64-v8a	9,495,801	-16,098
android	jsc	armeabi-v7a	8,273,423	-13,769
android	jsc	x86	9,433,588	-17,881
android	jsc	x86_64	10,026,574	-16,118

Base commit: df0b6900eca873417c867483b719e8e892a4b75d Branch: main

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	n/a	--

Base commit: df0b6900eca873417c867483b719e8e892a4b75d Branch: main

[facebook-github-bot]

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @gabrieldonadel in 4b9382c250261aab89b271618f8b68083ba01785.

^{When will my fix make it into a release? | Upcoming Releases}