[SYCL][NATIVECPU] async ops, wait for dependencies in threads

[uwedolinsky]

Makes most operations including memory copies asynchronous except enqueueBufferMap

Worker threads wait for dependent events instead of the main thread.

The state struct is now constructed by the threads instead of being constructed by the main thread and copied which

1. reduces the capturing overhead in the enqueue lambda
2. enabled removing mutable from enqueue lambda

Also removing #ifdef NATIVECPU_USE_OCK