Reverts "[iOS] Full keyboard access scrolling (#56606)"

[auto-submit]

Reverts: #56606

Initiated by: LongCatIsLooong

Reason for reverting: flutter/flutter#159456

Original PR Author: LongCatIsLooong

Reviewed By: {chunhtai, cbracken}

This change reverts the following previous change:
This PR adds basic FKA scrolling support: when the iOS focus (the focus state is maintained separately from the framework focus, see the previous PR) switches to an item in a scrollable container that is too close to the edge of the viewport, the container will scroll to make sure the next item is visible.

Previous PR for context: #55964

Screen.Recording.2024-11-18.at.1.48.19.PM.mov

Why the UIScrollView subclass in the focus hierarchy

The iOS focus system does not provide an API that allows apps to notify it of focus highlight changes. So if we were to keep using the transforms sent by the framework as-is and not introducing any UIViews in the focus hierarchy, the focus highlight will be positioned at the wrong location after scrolling (via FKA or via framework). That does not seem to be part of the public API and the focus system seems to only know how to properly highlight focusable UIViews.

Things that currently may not work

1. Nested scroll views (have not tried to verify)

The UIScrollViews are always subviews of the FlutterView. If there are nested scrollables the focus system may not be able to properly determine the focus hierarchy (in theory the iOS focus system should never depend on UIView.parentView but I haven't tried to verify that).

2. If the next item is too far below the bottom of the screen and there is a tab bar with focusable items, the focus will be transferred to tab bar instead of the next item in the list

Video demo (as you can see the scrolling is really finicky):

Screen.Recording.2024-11-18.at.2.09.09.PM.mov

I've tried doing the same thing using a UITableView with similar configurations but it seems to have the same problem. I'll try to dig a bit deeper into this and see if there's a workaround.

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.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or the PR is test-exempt. See testing the engine for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

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