Support eye tracking when running on visionOS or iOS

[stuartmorgan-g]

In initial testing of running iOS applications on the visionOS simulator, the most noticeable issue is that controls don't respond to eye tracking.

This is likely the same underlying feature as #55809, but filing separately since there may be some differences in what exactly is needed, so tracking both work and votes separately may be helpful.

[jmagman]

Looks like this will also be relevant on iOS:

Eye Tracking Comes to iPad and iPhone

Powered by artificial intelligence, Eye Tracking gives users a built-in option for navigating iPad and iPhone with just their eyes. Designed for users with physical disabilities, Eye Tracking uses the front-facing camera to set up and calibrate in seconds, and with on-device machine learning, all data used to set up and control this feature is kept securely on device, and isn’t shared with Apple.
Eye Tracking works across iPadOS and iOS apps, and doesn’t require additional hardware or accessories. With Eye Tracking, users can navigate through the elements of an app and use Dwell Control to activate each element, accessing additional functions such as physical buttons, swipes, and other gestures solely with their eyes.

https://www.apple.com/newsroom/2024/05/apple-announces-new-accessibility-features-including-eye-tracking/

[stuartmorgan-g]

This is likely the same underlying feature as #55809

I'm less convinced that this is the case having looked into it a bit more; there are new APIs in iOS 17, including in UIKit, that are about "hover", so it seems to be a different thing than tablet hover support. It's not clear that UIKit provides any mechanism for providing these new hover regions without mapping them 1:1 with UIViews, and if that's the case it would make Flutter support extremely difficult.

[SilverFruity]

I have already implemented Flutter support for VisionOS Eye Tracking using SemanticsNode, referencing the WebKit implementation. It's a compact codebase developed on Flutter 3.7.3. Due to certain circumstances, I currently can't migrate it to the latest Flutter version. If you're interested, I would be happy to open a PR.