tools/sched_ext: Sync with scx repo

Synchronize with https://github.com/sched-ext/scx

 at dc44584874f0 ("kernel:
Synchronize with kernel tools/sched_ext").

- READ/WRITE_ONCE() is made more proper and READA_ONCE_ARENA() is dropped.

- scale_by_task_weight[_inverse]() helpers added.

- Enum defs expanded to cover more and new enums.

- Don't trigger fatal error when some enums are missing from kernel BTF.

Signed-off-by: Tejun Heo <tj@kernel.org>