[PJRT:CPU] Provide a compile-time thread pool.
[PJRT:CPU] Provide a compile-time thread pool.

The OneDNN matmul rewriter starts a thread pool if one wasn't provided as a compile option, spawning many threads per compilation. If we pass a preexisting thread pool, we can save the cost of creating and tearing down threads.

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/9666 from ROCm:ci_fused_conv 8792f892770aba54e38a5352d9bec1d003e341d3
