Xamarin - update references - EntityFramework.Docs

[wadepickett]

Xamarin should no longer be referred to and we should refer to or direct to Maui instead:
https://learn.microsoft.com/en-us/dotnet/maui/what-is-maui?view=net-maui-9.0

In the https://github.com/dotnet/EntityFramework.Docs repo:

Remove all references to "Xamarin" or update to ".NET Multi-platform App UI (.NET MAUI)" for first reference and ".NET MAUI" for following references in the same doc.
If a topic centers on .NET MAUI and requires a complete rewrite rather than just an updated link or reference update, and/or requires a code sample update, AND we decide not to retire or archive it as the solution, then identify it here and then create a new tracking issue for that work.

Notify David Britch when complete.

Currently there are around 9 files referencing "Xamarin" and some app samples

See also:
#34324, #34325 for AspNetCore.Docs repo efforts
#34326 for the AspNetDocs repo effort.