Button should check RoutedEventArgs.Source before handling keys

[amwx]

Describe the bug

Reported in amwx/FluentAvalonia#591.

Placing a text control into an Expander header does not allow spaces. The cause is the Button that is found in the Expander's header (which is part of the template for my SettingsExpander control in the referenced issue) is consuming this event and the TextBox never sees it.

I looked at WPF source, they do a check in ButtonBase to see if the event source is the button and only handle it in that case - Avalonia should do the same check.

https://github.com/dotnet/wpf/blob/0628a7722ccdc47ebe66beb5eb8cee756d05f7d9/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/ButtonBase.cs#L612-L647

To Reproduce

Add a TextBox to an Expander and try to type text with spaces. Only the text will be entered, the space key will open/close the expander.

Expected behavior

No response

Avalonia version

11.1-rc1

OS

Windows

Additional context

No response