fix(ios): keep a zoomed ScrollView usable when its content size changes

[mifi]

Summary:

RCTScrollViewComponentView's _containerView is also the view UIScrollView zooms (viewForZoomingInScrollView:), so while the user is pinch-zoomed in it carries a scale transform. On every content size change updateState:oldState: assigned _containerView.frame, which is undefined behavior for a view with a non-identity transform (in practice UIKit shrinks the view's bounds by the zoom scale), and it also handed the unzoomed size to the UIScrollView as contentSize.

Visible result: pinch-zoom into a ScrollView, then change its size (rotate the device, or change the layout around it). The scrolled position jumps, and the content can no longer be zoomed all the way out; it stays stuck in a corner until the user zooms out and resizes again.

This lays the container out through bounds and center instead, and gives the scroll view the zoomed content size, which is what UIScrollView itself keeps contentSize at while zooming. With zoomScale == 1 the result is identical to before. In RTL, where the container carries a flip transform, bounds/center produce the same frame the old assignment did.

Changelog:

[IOS] [FIXED] - Pinch-zoomed ScrollView no longer breaks (position jump, cannot zoom back out) when its size changes

Test Plan:

1. Run the reproducer at https://github.com/mifi/reproducer-react-native (a zoomable ScrollView whose height changes on a button press, or rotate the device).
2. Zoom in, pan, resize. Before: position jumps and the content can no longer be zoomed out fully. After: zoom scale is kept and the content can be zoomed back out to fill the ScrollView.
3. Unzoomed ScrollViews (RNTester ScrollView examples, including RTL) behave as before.

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Generated by Claude Code