Flux - soft inpainting via differential diffusion (#9268)

* Flux - soft inpainting via differential diffusion

* .

* track changes to FluxInpaintPipeline

* make mask arrangement simplier

* make style

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Co-authored-by: YiYi Xu <yixu310@gmail.com>
Co-authored-by: Álvaro Somoza <asomoza@users.noreply.github.com>
Co-authored-by: asomoza <somoza.alvaro@gmail.com>