Fix WrapPanel when ItemWidth < Available Size

[SuperJMN]

What does the pull request do?

Fixes WrapPanel when ItemWith < Available Size.

What is the current behavior?

Children aren't arranged correctly. They become invisible.

What is the updated/expected behavior with this PR?

Children should display.

How was the solution implemented (if it's not obvious)?

Changing the ArrangeOverride method.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0053607-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

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[SuperJMN]

@SuperJMN,

Please read the following Contributor License Agreement (CLA). If you agree with the CLA, please reply with the following:

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[MrJul]

Thank you for your contribution!
Can you please add a matching unit test?

[stevemonaco]

See #16191 and #16487 for related. WrapPanel port from WPF doesn't work in all cases because Avalonia arrange doesn't follow WPF rules. This part can't be fixed until v12 since it's a major breaking change and it was unclear from the team which approach was preferred.