[iOS] Fix SafeArea arrange insets using incorrect bounds in SizeThatFits

[Copilot]

Note

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Description

Fixes an issue where SafeArea arrange insets were incorrectly calculated due to a mismatch between the measure and arrange phases in MauiView on iOS.

Problem

The issue occurred because SizeThatFits and LayoutSubviews were using inconsistent bounds calculations for SafeArea:

1. SizeThatFits: Measured content without considering SafeArea insets, returning a size based on content alone
2. LayoutSubviews: Applied SafeArea insets during arrange using AdjustForSafeArea, reducing the available space

This mismatch caused the parent view to allocate space based on the unadjusted size, but the child layout would arrange within the SafeArea-adjusted (smaller) bounds, leading to incorrect layout positioning.

Example

Given this XAML:

<VerticalStackLayout x:Name="layout" 
                     BackgroundColor="Purple" 
                     IgnoreSafeArea="False" 
                     VerticalOptions="Start" 
                     IsClippedToBounds="True">
    <Entry x:Name="entry" 
           BackgroundColor="Green" 
           Text="Hello there" />
</VerticalStackLayout>

The Entry would be positioned incorrectly within the VerticalStackLayout due to the bounds calculation mismatch.

Solution

Modified SizeThatFits in MauiView.cs to:

1. Detect SafeArea requirements: Uses the same logic as AdjustForSafeArea to determine when SafeArea should be applied
2. Adjust measurement constraints: Reduces the available measurement space by SafeArea insets before measuring content
3. Return correct total size: Adds back the SafeArea insets to the measured size so the parent allocates the correct total space

This ensures consistency between the measure and arrange phases, with both accounting for SafeArea insets appropriately.

Changes

• Modified SizeThatFits method in src/Core/src/Platform/iOS/MauiView.cs
• Added comprehensive UI test case Issue24246 to validate the fix
• Minimal changes: 30 lines added, 1 removed in the core implementation

Testing

• Created test case reproducing the original problem scenario
• Verified compilation and build success across multiple target frameworks
• Ensured no regressions in non-SafeArea scenarios
• Applied code formatting and style guidelines

Fixes #24246.

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