[code analysis] potential bug with implicit using directives

[khemichew]

C# introduced implicit using directives in C# 6.0, but code analysis with Roslyn requires the using directives to be specified upfront for it to be able to deduce the types from the namespace included.

https://learn.microsoft.com/en-gb/dotnet/core/project-sdk/overview#implicit-using-directives

An example includes:

public class C {
    public void M() {
        int x = 0;
    }
}

which would compile without the using System; directive, but:

public class C {
    public void M() {
        Int32 x = 0; // will not compile
    }
}

with error CS0246: The type or namespace name 'Int32' could not be found (are you missing a using directive or an assembly reference?)

To make the code compile, the directive should be added:

using System;

public class C {
    public void M() {
        Int32 x = 0; 
    }
}

A task is to explore how this would affect code analysis: the solution would involve discovering if the project has the ImplicitUsings setting enabled, and explicitly adding the using statements to the compilation before analysis takes place.