Update and fix Windows CI builds

- boost-spirit dependency needed to be installed
- Visual Studio wanted boost/filesystem.hpp included in more places
- a deprecated enum was removed from new versions of boost, so we use
  its replacement enum now
- vcpkg repository is now pinned to a commit where boost 1.84 libraries
  work smoothly, there should be no more surprises
- vcpkg dependencies now cache, so successive CI runs are dramatically
  faster
- for win-scons, we need to use 'call' in our batch script to source
  vcvarsall.bat
- I updated the includepath and libpath we pass to win-scons to match
  reality, but it still can't find any vcpkg libraries. This will need
  further sleuthing

src/scenedit/scen.fileio.cpp

@@ -6,6 +6,7 @@
 #include <fstream>
 #include <iomanip>
 #include <boost/filesystem/operations.hpp>
+#include <boost/filesystem.hpp>
 #include "scen.fileio.hpp"
 #include "scen.keydlgs.hpp"
 #include "gfx/gfxsheets.hpp"