WebNN and StableHLO opset compatibility

[anssiko]

From w3c/machine-learning-charter#28:

We explored areas of collaboration with the OpenXLA project during our WebML WG Teleconference – 17 November 2022.

We have done a small-scale WebNN op compatibility exploration with XLA-HLO in 2020. During our call today there was an agreement we should consider revising this study with StableHLO that targets feature completeness EOY 2022. A good start for this effort would thus be ~Q1-Q2'23.

StableHLO roadmap is now public and I expect we can commence with this effort soon after our revised charter is operational Q2 2023. I label this as v2 to signal we do initial CR ("v1") first.

FYI @burmako