[Attention processor] Create SDPA versions of attention processors

[sayakpaul]

diffusers currently supports the following PT 2.0 variant of attention processors

• AttnProcessor => AttnProcessor2_0
• AttnAddedKVProcessor => AttnAddedKVProcessor2_0

The following are not supported:

• SlicedAttnProcessor
• SlicedAttnAddedKVProcessor
• LoRAAttnProcessor
• CustomDiffusionAttnProcessor

We should add SDPA versions of the above processors. This essentially eliminates the need to use xformers.

[github-actions]

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