Fix Flax flip_sin_to_cos

[akashgokul]

Adding flip_sin_to_cos arg for FlaxTimesteps and passing it to get_sinusodial_embeddings.

Currently, FlaxTimesteps hardcodes the order of the sin and cosine embeddings (1). However, in the UNet2DConditionModel the order is an argument (set to True when loaded from StableDiffusion pretrained ckpt/config) which is currently not supported in Flax.

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[kashif]

thank you @akashgokul I actually had a look at this and it's good from my end! Unet is the only place where the sin/cos is flipped so that is also fine. Let me update the branch and run the tests.