Prevent infinite recursion in Solution parser when a project is nested under itself

We don't check for invalid project nestings in the solution file, so it's possible to create a solution that crashes MSBuild with stack overflow:

https://github.com/Microsoft/msbuild/blob/xplat/src/XMakeBuildEngine/Construction/Solution/ProjectInSolution.cs#L393

An example solution is:
https://github.com/dotnet/corefx/blob/f6ab339f446e37505f93ef9f430801fa1dcc05b8/src/System.Collections.Immutable/System.Collections.Immutable.sln#L40-L41

Note that we should check for indirect recursion as well (loops).