Add optimized_portable_kernels test

[swolchok]

Make sure we test the optimized versions of portable kernels even if they are shadowed by optimized implementations. Intended to support #9432.

[swolchok]

Stack from ghstack (oldest at bottom):

• Implement unary_ufunc functions using elementwise_util #9386
• Add mixed integer precision test for op_mul #11206
• Add SupportedTensorDtypes::BOOL #9584
• relax tolerances for all unary float ops #9585
• Add vectorization in elementwise_util #9432
• -> Add optimized_portable_kernels test #11205
• Add vectorized_math.h #11204

[pytorch-bot]

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