Add sbbsexec.dll project (again)

Regenerated for MSVC2019, the Synchronet virtual UART/FOSSIL driver (VDD) can be built from Visual Studio again (the makevdd.bat can probably go away now). I haven't had an MSVC project to build this DLL since the old MSVC 6.0 sbbsexec.dsp file.

A few oddities about this project:
1. xpdev files had to directly included/compiled in this project rather than linking with the xpdev_mt.lib because __stdcall calling convention is required for compatibility with ntvdm.lib and xpdev_mt.lib is built using __cdecl calling convention (the default). Rather than re-introducing the calling convention game-playing that I just recently removed (e.g. #define DLLCALL), just build the required xpdev files directly as part of this project. Perhaps there is a more elegant solution that I'll revisit later.

2. The absolute path of my install Windows 10 SDK directories had to be specified (for include and library paths) to find vdd_svc.h and ntvdm.lib. Weird thing is that I didn't have to do anything hacky like this with the command-line/batch file build method. Again, there's probably a better solution I'm not seeing. But as is, this project might not build on other systems.

So why use this rather than the brute-force batch file (makevdd.bat)? Well, this should be a little easier to get into CI/nightly builds and the resulting release build was 30KB (instead of 150KB), so that's good.

Before:
           1AA00 size of code
            AA00 size of initialized data
               0 size of uninitialized data
After:
            4C00 size of code
            2A00 size of initialized data
               0 size of uninitialized data

Those default DLL project build options include some good optimization flags apparently.