Arrange content based on arrangement bounds rather than viewport bounds

[hartez]

Description of Change

The final content arrangement was being done using the viewport bounds, which are offset by the scroll distance. The arrangement should be done by the ScrollView's arrangement bounds, as passed into the CrossPlatformArrange() method.

Issues Fixed

Fixes #18513

[PureWeen]

Tested against our template and it looks like the scroll bars return

https://github.com/dotnet/maui/tree/fix-18513-repro

[PureWeen]

D:\a_work\1\s\src\Core\src\Handlers\ScrollView\ScrollViewHandler.iOS.cs(350,8): error CS0128: A local variable or function named 'contentSize' is already defined in this scope [D:\a_work\1\s\src\Core\src\Core.csproj::TargetFramework=net8.0-maccatalyst]
D:\a_work\1\s\src\Core\src\Handlers\ScrollView\ScrollViewHandler.iOS.cs(348,32): error CS0104: 'Point' is an ambiguous reference between 'System.Drawing.Point' and 'Microsoft.Maui.Graphics.Point' [D:\a_work\1\s\src\Core\src\Core.csproj::TargetFramework=net8.0-ios]
D:\a_work\1\s\src\Core\src\Handlers\ScrollView\ScrollViewHandler.iOS.cs(350,8): error CS0128: A local variable or function named 'contentSize' is already defined in this scope [D:\a_work\1\s\src\Core\src\Core.csproj::TargetFramework=net8.0-ios]
36 Warning(s)
4 Error(s)

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

/rebase

[tj-devel709]

I applied this PR and was able to see that my scrollviews that used to come too far down on the screen are respecting the bottom safe areas as I would expect!