Refactor elementwise_util: create variants with out_dtypes in template argument list

[swolchok]

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[swolchok]

Stack from ghstack (oldest at bottom):

• Add vectorization in elementwise_util #9432
• BroadcastIndexesRange: leading 1s don't require true broadcasting #9431
• Save some size in dtype_util when dtype selective build is not in use #9842
• Migrate elementwise_util callers to the variants with out_dtypes in template arguments #9841
• RFC: Specialize for non-mixed-dtype in elementwise_util #9388
• -> Refactor elementwise_util: create variants with out_dtypes in template argument list #9387
• Add build_optimized_size_test.sh #9840
• set INTERFACE_LINK_LIBARIES for extension_threadpool #9839
• Fix build gating on optimized_portable_kernels #9838
• Make PyTorch headers available in optimized_portable_kernels, define ET_USE_PYTORCH_HEADERS #9384

[pytorch-bot]

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