[ios][autocorrection]disable auto-correction highlight in iOS 17

[hellohuanlin]

This PR disables the "auto-correction highlight" feature in iOS 17.

This feature was introduced in flutter/flutter#45354 and #13959 (CC: @LongCatIsLooong who was the original author)

I have created a new issue to find other approaches to re-enable this feature.

Note that "auto-correction" itself still works, it's only the "highlight" part is disabled:

• iOS 16 with highlight:
  https://github.com/flutter/engine/assets/41930132/2fe7bbf6-f2db-4212-a020-e420ad8dd5e6

• iOS 17 without highlight:
  https://github.com/flutter/engine/assets/41930132/34f34743-6bef-4e93-80d2-d04c92ba59bf

Why disable this feature?

The original PR uses UITextInput::firstRectForRange API for auto-correction, since Apple does not provide any other API when auto-correction should show up, so the original PR used this API as a workaround.

In iOS 17, Apple changed a few UITextInput behaviors:

• UIKit does not query UITextInput::firstRectForRange for text range of the auto-corrected word any more.
• But instead, it repeatedly queries every single character of the current word (after entering or deleting a character), regardless whether the word should be auto-corrected or not.

I have tried all other UITextInput APIs that takes a text range, and none are suitable for auto-correction feature. As a result, I have to disable this feature for iOS 17 for now.

List which issues are fixed by this PR. You must list at least one issue.

Fixes flutter/flutter#128406

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
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• I listed at least one issue that this PR fixes in the description above.
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• I signed the CLA.
• All existing and new tests are passing.

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[LongCatIsLooong]

The text highlight on iOS 17 at the top left corner looks out of place. If possible that should be fixed as well?

[hellohuanlin]

@LongCatIsLooong Yes, that's the next thing I plan to do. Will do more research, but this one is more urgent.

[stuartmorgan]

Nit: iOS 17+

[stuartmorgan]

Please add a test of that.

[justinmc]

+1 to testing that it's disabled in iOS 17 if possible.

What's your plan for hiding the autocorrect highlight altogether? I guess it depends on merging this PR first? Because I would almost say that showing the highlight on the last character could be better than showing the highlight in the top left corner.

[hellohuanlin]

What's your plan for hiding the autocorrect highlight altogether?

@justinmc I plan to hide the top highlight as well.

While I was investigating that, I found something interesting - even in iOS 16, the top highlight shows up, but with just a single char length, rather than a word length. It's just that now in iOS 17 this problem becomes more noticeable. Still I'm surprised that no one notice it before. I created this issue with more details.

[hellohuanlin]

Because I would almost say that showing the highlight on the last character could be better than showing the highlight in the top left corner.

@justinmc to clarify, the highlight on the last char shows up on every keystroke. So it is likely a "deal breaker" for iOS apps. Here's a video of it: flutter/flutter#128406 (comment)

On the other hand, the top left corner highlight only shows up for misspelled word. It's much less frequent, but still very bad though, so its the next thing in my list :)

[justinmc]

Got it, thanks for the clarification. I agree that this is an improvement then. LGTM 👍

[stuartmorgan]

LGTM

As soon as this rolls into the framework tree and has been confirmed working on Flutter master, please make sure to request a cherry pick to beta.