Generated Visual Studio project should group build files and source file separately

Currently the `build.gradle` file added to the project file are grouped together as "Source Files". Instead, group the build files in a separate group.

Start by locating the generator for the Visual Studio project and inspect how the mentioned build.gradle file is assigned to the "Source Files" group. Done means generated projects place build files in a separate group while source files remain in "Source Files"; no specific test is named in the issue.

Written by the indexing model from the issue text.