Proj0219: Packable projects should be libraries

Creating NuGet packages for project files other than libraries is so rare that we consder it to be a mistake.

If your project is the exception to this rule, you should disable this rule for the reported project.

Non-compliant

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <OutputType>Exe</OutputType>
    <IsPackable>true</IsPackable>
  </PropertyGroup>

</Project>

Compliant

<Project Sdk="Microsoft.NET.Sdk">
 
 <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <OutputType>Library</OutputType>
    <IsPackable>true</IsPackable>
  </PropertyGroup>

</Project>