* Switch to yearless copyright per FB policy
* Fix up SPDX-License-Identifier lines in `contrib/linux-kernel` sources
* Add zstd copyright/license header to the `contrib/linux-kernel` sources
* Update the `tests/test-license.py` to check for yearless copyright
* Improvements to `tests/test-license.py`
* Check `contrib/linux-kernel` in `tests/test-license.py`
Expose the zstd headers in `include/linux` to avoid struct duplication.
This makes the member names not follow Kernel style guidelines, and
exposes the zstd symbols. But, the LMKL reviewers are okay with that.
Add the kernel wrapper API. This keeps the same API and semantics as the
existing kernel API with name changes to be more kernel style and avoid
symbol collisions with zstd.
