initial SYCL build system and examples

[yxlao]

• Initial build system with SYCL
• Python unit test, C++ unit test, C++ example, C++ linkage with as third-party lib are all working
• CPU only, not tested with iGPU or dGPU
• See 3rdparty/README_SYCL.md on how to set up the SYCL environment

This change is 

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[benjaminum]

Reviewable status: 0 of 37 files reviewed, 6 unresolved discussions (waiting on @benjaminum, @ssheorey, and @yxlao)

---

3rdparty/find_dependencies.cmake line 1377 at r6 (raw file):

        message(STATUS "Using OneAPI packages from: $ENV{ONEAPI_ROOT}")
    else()
        message(FATAL_ERROR "OneAPI packages not found. Please run `source /opt/intel/oneapi/setvars.sh`")

Just a comment, the env var is not set for the conda distribution and is not used to find the packages as far as I know.
We can update when the conda problems with oneAPI are solved.

[yxlao]

Reviewable status: 0 of 37 files reviewed, 6 unresolved discussions (waiting on @benjaminum and @ssheorey)

---

3rdparty/find_dependencies.cmake line 1377 at r6 (raw file):

Previously, benjaminum (Benjamin Ummenhofer) wrote…

Just a comment, the env var is not set for the conda distribution and is not used to find the packages as far as I know.
We can update when the conda problems with oneAPI are solved.

Sounds good, I'll remove this check for now.