reasons for why `is_compatible` may return false

I think I agree that since there are a few different reasons for why `is_compatible` may return false, it would be useful to have a way to expose the reason, I'm not sure how useful it would be as a mechanism for dispatching different kernels, but it could at least be a useful debug feature, to be able to identify exactly why the kernel couldn't be run on a certain device. Saying that, if we were to do this, I think that could be a different PR that doesn't need to hold up this one.

_Originally posted by @AerialMantis in https://github.com/KhronosGroup/SYCL-Docs/pull/381#discussion_r1146347373_

Review the discussion from pull request 381 and identify the distinct reasons that `is_compatible` may return false. Clarify whether exposing those reasons is intended as a separate debugging feature, then define the expected interface and completion criteria before implementation.

Written by the indexing model from the issue text.