[xla:gpu] Create a non-atomically upgradeable reader mutex lock that acquires...

[xla:gpu] Create a non-atomically upgradeable reader mutex lock that acquires and releases the lock via RAII

Runtime autotuning needs to be protected by a writer mutex lock. However GpuExecutable runs under a reader mutex lock, so it needs to be upgraded to a writer lock whenever autotuning happens.

PiperOrigin-RevId: 510509236