Warning for properties defined in project but never read

Since MSBuild allows defining any property, it's very common to define the wrong property accidentally--either via typo, or by guessing a wrong name. When this happens, it's rarely clear what has gone wrong.

If there was a warning that fired when a project defined a property that was never read, that could help. Ideally it would also do some sort of edit-distance based "did you mean X, Y, or Z?" like many command line applications do.

This probably should apply only to the project file itself. It's reasonable for `Directory.Build.props` and friends to define properties for all projects that are consumed by only some of them.

Evidently cmake has this: https://twitter.com/johnregehr/status/1134108018738524167

Start by tracing how properties are defined and read in an MSBuild project file; the issue does not name implementation files or tests. Compare the requested behavior with the stated Directory.Build.props exception and the linked CMake example. Done means unused properties in the project file produce a warning, with a considered edit-distance suggestion where appropriate.

Written by the indexing model from the issue text.