Projects that differ only by the SolutionConfiguration property are hard to diagnose

[rainersigwald]

I just chased down a build where the build structure was

graph TD
build.proj --> Solution.sln
build.proj --> Solution.distinct.sln
Solution.sln --> Library.csproj
Solution.distinct.sln --> Distinct.csproj
Solution.distinct.sln --> Distinct.Tests.csproj
Distinct.Tests.csproj --> Library.csproj

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In this configuration, Library.csproj builds twice, with distinct SolutionConfiguration property XML values. But since SolutionConfiguration is usually the same across a whole build (it's computed at the solution level and passed to all child projects and not usually mutated), this tool currently elides it entirely--so it was not at all obvious that a difference in SolutionConfiguration was the property difference causing a build race, even looking at the output.

We should add a case that detects distinct SolutionConfigurations and if there is more than one value, report it everywhere or at least flag the second discovered SolutionConfiguration in the output.