UWP dependencies

The ANGLE UWP runtime is committed under angle. The package also uses:

LOVE_UWP_ROOT: caorthann-celt/love-xbox-uwp on the gen1recomp branch.
UWP_SDL2_ANGLE_ROOT: SDL2 built by scripts/build-sdl2-angle.ps1.
VCPKG_ROOT: the UWP codec, font, compression, and audio runtimes used by LÖVE.

SDL headers, import library, and DLL must come from the same build. Runtime DLLs stay inside the installed package.