Remove support for multiple C++ standards in the same CMake build

[bernhardmgruber]

Our CMake scripts support creating targets for multiple different C++ standard versions in the same build directory. This ignores common practice of setting a single C++ standard in CMake using CMAKE_CXX_STANDARD (or CMAKE_CUDA_STANDARD), which is misleading for new comers expecting a standard CMake workflow, and incurs maintainance cost and overhead on our side, whenever we have to touch this machinery or configure builds ourselves outside presets.

Because there is no longer a need to configure for multiple C++ standards in the same build, I propose to remove this "feature" and just depend on CMAKE_CXX_STANDARD and CMAKE_CUDA_STANDARD.

As a starting point, this concerns at least the following cmake variables (to be removed):
CUB_ENABLE_DIALECT_CPP17
CUB_ENABLE_DIALECT_CPP20
CUB_CPP_DIALECT_OPTIONS
THRUST_CPP_DIALECT
CCCL_KNOWN_CXX_DIALECTS
cudax_CPP_DIALECT_OPTIONS
CUB_ENABLE_CPP_DIALECT_IN_NAMES

Any xxx.compiler_interface_cpp${dialect} can be collapsed to a single target as well.

Grep for any use of the word DIALECT or 17 and 20 in the CMake scripts.