feat(xUnit): Add xUnit Test Project to Template Options

[DevTKSS]

GitHub Issue (If applicable): closes #1258

PR Type

What kind of change does this PR introduce?

• Feature

What is the current behavior?

only none, unit(=> NUnit) Test Projects available to get from the Templates

What is the new behavior?

• adds Option for xUnit Test
• Provides Quick Links in the added Project how to use this with:
  • Microsoft Test Platform
  • dotnet SDK 8/9/10+
• included by default Shouldly instead of FluentAssetions and included this Package in the xUnit conditionals

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] Associated with an issue (GitHub or internal)

Other information

See for more information about my Reasons to default to Shouldly instead of FluentAssertions:

• #1605

Internal Issue (If applicable):