Use D3D12_SDK_VERSION macro consistently across samples, instead of explicitly setting the version in source files.

Many samples explicitly reference the d3d12 sdk version

extern "C" { __declspec(dllexport) extern const UINT D3D12SDKVersion = 618; }

Whenever the SDK version is updated, the source files must also be updated, which is a tedius and annoying process. If, instead, the version is set to D3D12_SDK_VERSION then samples will automatically use the correct version.

extern "C" { __declspec(dllexport) extern const UINT D3D12SDKVersion = D3D12_SDK_VERSION; }

Example locations of this: (But there are many many more!)

https://github.com/microsoft/DirectX-Graphics-Samples/blob/b550a78e815bbc8b7a0fd948efab11c01d9a1ed2/Samples/Desktop/D3D12Raytracing/src/D3D12RaytracingHelloWorld/D3D12RaytracingHelloWorld.cpp#L20

https://github.com/microsoft/DirectX-Graphics-Samples/blob/b550a78e815bbc8b7a0fd948efab11c01d9a1ed2/Samples/Desktop/D3D12On7/src/D3D12On7.cpp#L17