design proposal: PJRT C API optional and experimental features

[Skye Wanderman-Milne]

Hi PJRT plugin authors + friends,

We'd like to introduce a structured way to handle optional and experimental features to the PJRT C API. This should hopefully make everyone's lives easier by clearly delineating what's most important to implement vs. leave unimplemented, and make sure there's graceful handling of unimplemented optional features. Brief design proposal here: https://docs.google.com/document/d/1PsSIkCbHujPfiZphyQ3U5wB9VGBLKBjxGrTtmziJwEw/edit

We're planning to implement handling of optional features in JAX first, but the mechanism is generic across frameworks.

We'd love any feedback you have on the proposal! Feel free to reply here or comment on the doc. 

Thanks,

Skye