Raise minimum requirements to C++17

[stotko]

C++17 has been released 5 years ago and the default compilers on Ubuntu 20.04 and Ubuntu 22.04 all support this standard. Support in CUDA has been added with CUDA 11.0 (released March 2020) and a potential future SYCL backend will require C++17 anyways. Furthermore, Ubuntu 18.04 will reach EOL soon in April 2023 and should not longer be used. Therefore, it makes sense to raise the requirements which will also simplify and unblock future developments.

New Requirements

• Drop Ubuntu 18.04 support (EOL in April 2023)

• GCC 7 -> 9, Clang 6 -> 10, MSVC 19.20 already sufficient

• CMake 3.15 -> 3.18 (CUDA support for C++17), also aligns with the requirements for the Clang CUDA compiler

• thrust 1.9.2 -> thrust 1.9.9

• CUDA 10.0 -> 11.0

Cleanups with C++17

• Library Code

  • [x] ~Use inline variables in limits -> unblocks header-only~
  • [x] ~Replace *::value by shorter *_v versions~
  • [x] ~Drop void_t in type_traits~
  • [x] ~Drop attribute.h and use native attributes~
  • [x] ~Drop STDGPU_HAS_CXX_17~
  • [x] ~Drop atomic backports in CUDA backend for CC 3.0 and lower (support removed with CUDA 11.0+)~
  • [x] ~Drop thrust workaround in memory~
  • [x] ~Simplify to_address implementation with if constexpr~
  • [x] ~Use std::byte over unsigned char in bit~
  • [x] ~Add noexcept qualifier to function signatures~

• CMake

  • [x] ~Drop custom generation of compile flags for CUDA architectures~
  • [x] ~Drop custom FindCUDAToolkit.cmake module~
  • [x] ~Drop workarounds in CUDA set_device_flags.cmake~