Remove minimum requirement for C# version 7

[bao7uo]

Adding explicit variable declarations for an out variable, instead of declaring them in the method call means that C# version 7 is not a minimum requirement, and different version of msbuild can be used. So this PR improves backward compatibility with earlier C# versions.

"Starting with C# 7.0, you can declare the out variable in the argument list of the method call, rather than in a separate variable declaration. " - https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/out-parameter-modifier