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.
14 jobs for master in 15 minutes and 35 seconds (queued for 18 seconds)
Status Job ID Name Coverage
  Build
passed #27814
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jsdoor-freebsd

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jsdoor-linux

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jsdoor-windows

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sbbs-freebsd

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sbbs-linux

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sbbs-windows

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sexpots-freebsd

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sexpots-linux

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sexpots-windows

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syncdraw-freebsd

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syncdraw-linux

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syncterm-freebsd

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syncterm-linux

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syncterm-windows

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