[RFC]: C API

[rscohn2]

I formatted Gengbin's C APi proposal as an RFC.

[garzaran]

Looks good.

[blazej-smorawski]

What's the device? We should be much more specific here. I think we don't have to cover this API. My proposal is to handle all device handles in ...Config APIs, so for example. For example passing users device to onecclCommInit would look like:

onecclCommConfig_t config = ONECCL_COMM_CONFIG_INITIALIZER;
config.sycl.queue = &queue;

onecclCommInitConfig(rank, size, ..., &config);

Similar pattern could be applied to onecclStreamCreate, so we could get rid of onecclCreateSyclStream which looks like a workaround rather than an elegant solution:

onecclStream_t stream;
onecclStreamConfig_t stream_config = ONECCL_STREAM_SYCL_CONFIG_INITIALIZER;
// or onecclStreamConfig_t config = ONECCL_STREAM_CONFIG_INITIALIZER;
config.sycl.queue = &queue;

onecclStreamCreateConfig(&stream, &config);