VS: Switch ZERO_CHECK to msbuild project ZERO_CHECK.proj

Previously, CMake wrote ZERO_CHECK.vcxproj to rebuild build system. However, msbuild doesn't need a C++ project (.vcxproj) for executing a script. This MR uses the support for building incrementally in MSBuild and replaces ZERO_CHECK.vcxproj by ZERO_CHECK.proj - an msbuild project.

Since ZERO_CHECK is internal to CMake, we also remove the project from .sln file. Note however that any build (or clean or rebuild) of the solution or any project invokes that on ZERO_CHECK.proj as the project is a dependency.

Topic-rename: vs-zero_check-proj