Move build system to CMake + skbuild

[oleksandr-pavlyk]

The assortment of remaining tasks to complete transition of DCPTL to cmake + skbuild.

• Enable sycl::program in libsyclinterface/tests/dpcpp_kernels.hpp.
• Add build system configuration to pyproject.toml (e.g. specify dependencies for building docs).
• cmake + skbuild should work with nightly sycl bundles
• Write coverage build driver (scripts/gen_coverage.py)
• Write docs driver (scripts/gen_docs.py)
• Write script to drive build with sycl nightly
• Ensure SDL flags are added to CMakeLists.txt
• Upstream change to skbuild to preserve symbolic link to components of versioned shared library
• Fix dpctl should not vendor versioneer, but use one from PyPI or conda-forge #651, make sure versioneer overrides dpctl/_version.py, a step which relies on using versioneer provided "build_py" step.
• Make sure pybind11 extension can be added to dpctl, which is the ultimate reason for this work

[oleksandr-pavlyk]

Versioneer does override dpctl/_version.py with changes from #746, but only for setup.py install command, not for setup.py develop. The issue #651 is separate and is not tied to this effort.

[oleksandr-pavlyk]

I filed scikit-build/scikit-build#625 to retain symbolic links for partially versioned aliases of the library, but because Python wheels do not support symbolic links yet, it is unlikely that the change is going to be adopted.

The only way forward for dpctl is to monkey patch skbuild.setuptools_wrap._copy_file function, since we target conda.