Background

This issue tracks one of the BuildCheck analyzers we would like to ship in-box with MSBuild.

Goal

Implement an analyzer with the following rule: The TargetFramework and TargetFrameworks properties should not be both set in outer builds.

Notes

Setting both properties leads to unexpected SDK behavior. It is not uncommon for developers to define one of them in a project file and the other in an imported file such as Directory.Build.props.