Ptxla sd training (#9381)
* enable pxla training of stable diffusion 2.x models.
* run linter/style and run pipeline test for stable diffusion and fix issues.
* update xla libraries
* fix read me newline.
* move files to research folder.
* update per comments.
* rename readme.
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Co-authored-by: Juan Acevedo <jfacevedo@google.com>
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
