Support for manual CLIP loading in StableDiffusionPipeline - txt2img. (#3832)
* Support for manual CLIP loading in StableDiffusionPipeline - txt2img.
* Update src/diffusers/pipelines/stable_diffusion/convert_from_ckpt.py
* Update variables & according docs to match previous style.
* Updated to match style & quality of 'diffusers'
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Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>