Targeting .NET 6.0 in Visual Studio 2019 is not supported

[workgroupengineering]

Describe the bug

Targeting .NET 6.0 in Visual Studio 2019 is not supported

To Reproduce
Steps to reproduce the behavior:

1. Build Avalonia in VS 2019

Expected behavior
Do not repoort warnings

Screenshots

Desktop (please complete the following information):

• OS: [e.g. Windows, Mac, Linux (State distribution)]
• Version [e.g. 0.10.0-rc1 or 0.9.12]

Additional context
Add any other context about the problem here.

[rstm-sf]

.NET 6 not supports in VS 2019 https://docs.microsoft.com/en-us/answers/questions/620284/how-to-target-net-60-with-visual-studio-2019.html

https://github.com/dotnet/core/blob/main/release-notes/6.0/known-issues.md#net-sdk

[maxkatz6]

We discussed it before, and .NET 6 advantages outweigh the fact you have to install VS2022.

Too bad if Microsoft decided to lock new SDK only for new VS, but it's not something we can deal with.

[llfab]

You may want to check this as an intermadiate solution: #7024

[mysteryx93]

With JetBrains Rider it supports .NET 6 without a hitch.