Users can add additional VS project configurations with their own
custom settings, but to support this workflow, we can't rely directly
on $(Platform) and $(Configuration), because VS needs those to be
both unique Configuration|Platform combos, and we need to allow for
different combos of Configuration|Platform to point to the same
scons build configuration.
GodotPlatform and GodotConfiguration properties lets us decouple from
the magic VS properties that we don't control, so users can add
however many Platform|Configuration combos they want and still
point to a specific GodotPlatform|GodotConfiguration build config.
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