[thread-qos] Research what is available from various platforms, and how this could map into definitions

To know what is possible with a mostly generic we need to map out what various platforms support.

And what sort of combinations would be possible with these; what would it map to, or what would it make sense to map it to.

Part of this should also be to look at some prior art around thread type / QoS APIs to see what other projects are defining.