Add Links to WPF and WinUI Equivalent Doc Pages

[robloo]

Until Avalonia docs improve, adding direct links at the top of each page to the WPF and WinUI equivalent pages is going to help new users. I have seen several concerns about docs and this is a quick fix to help. There should be no licensing concerns by provided a hyperlink to external docs.

There is risk this might actually confuse people even more as Avalonia controls aren't 100% the same. So it needs to be discussed a bit first. However, it also should help give ideas and code to try.

[robloo]

Seems like there is no interest in doing this. Will close.