[RFC] Intel GPU integration

[Zantares]

Hi all,

Here's Teng, Lu from Intel. Recently Intel has experimental released Intel® Extension for OpenXLA* based on PJRT to support runing applications on Intel GPU. To follow the new XLA GPU roadmap and maximize the capabilities of OpenXLA, we would like to upstream the related changes inside Intel® Extension for OpenXLA* to OpenXLA to make Intel GPU as in-tree build device.

The main RFC is submitted here, and we will have follow-up RFCs to flesh out specific details. Hope to get your suggestion for this proposal, thanks!