Introduce a clGetDeviceAndHostTimer analogue

[kbenzie]

intel/llvm#7526 introduces the ability to query the device timestamp, this is an analogue of clGetDeviceAndHostTimer. We should also introduce this into the UR spec.

[veselypeta]

We should make pHostTimer & pDeviceTimer optional parameters so that urDeviceGetGlobalTimestamps can be used as an anologue of both clGetDeviceAndHostTimer and clGetHostTimer.

uint64_t device_time;
uint64_t host_time;
urDeviceGetGlobalTimestamps(device, &device_time, &host_time);  // analogue of clGetDeviceAndHostTimer
urDeviceGetGlobalTimestamps(device, nullptr, &host_time);       // analogue of clGetHostTimer
urDeviceGetGlobalTimestamps(device, nullptr, nullptr);          // does nothing

[kbenzie]

Is this to match the behaviour in intel/llvm#7526 ? Does the OpenCL analogue also make these optional?

[veselypeta]

They are required arguments in OpenCL, but the OpenCL plugin in PI does the following:

  if (DeviceTime) {
    uint64_t dummy;
    clGetDeviceAndHostTimer(deviceID, DeviceTime,
                            HostTime == nullptr ? &dummy : HostTime);

  } else if (HostTime) {
    clGetHostTimer(deviceID, HostTime);
  }

[kbenzie]

Okay, so its to match the PI behaviour 👍