HIP language support

[MathiasMagnus]

Please support HIP as a C++ dialect based off of the existing CUDA support.

HIP is AMD's single-source GPGPU API, which is heavily influenced by CUDA, to extents that the two are nearly source compatible. Although not strictly related, but CMake 3.21 recently landed HIP language support, so the .cpp extension need not be overloaded anymore for HIP source code. HIP shares the same keywords and semantics as CUDA, without the <<<>>> operator and instead uses a macro for kernel launch, hipLaunchKernelGGL().

ps.: HIP also has a pure host-side implementation using C++17 with a touch of OpenMP under the name HIP-CPU. It is an invaluable tool to run device code on machines without compatible GPUs and to debug the code using ordinary CPU debugger. (Throwing structured exceptions in GPU code is fun.) In such cases, the builds would set source file language to CXX instead of HIP. It would be great if cpptools would function properly in both cases and pick up source file language based on CMake config. (IntelliSense workes flawlessly with Main.cpp and HIP-CPU. The editor however seems to pick up source language based on file extension. Now Main.hip is all white if not configured in settings.json, but even then include paths will not be picked up.)

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