[BUG] Uno.Extensions.Validation for Options not available in App.caml.cs hostbuilder

[DevTKSS]

Description

• [Docs][Validation] Docs Information/Guidance missing/incomplete: Missing UnoFeatures Entry for (any) Validation, tell about need for manual Package import! Not working docs! unoplatform/uno.extensions#2883

Steps to Reproduce

1. Create a new uno app
2. Try following the uno docs for adding the UseValidation() in the hostbuilder
3. Its not resolving.

Affected platforms

Skia Desktop, Android, iOS, MacOS, Windows, GTK, Linux Framebuffer, WPF, WebAssembly

Did you find any workaround?

• use the regular Microsoft DI/OptionsBuilder
• In Uno: Instead of adding Validation into <UnoFeatures> we need to add the PackageReference manually the "old" way

Relevant log output