Mostly sync BlasKernel.cpp with ATen ReducedPrecisionGemvFastPathKernel

Pull Request resolved: #10868

The two files were similar, but diverged due to recent changes. Since we have sharing of PyTorch headers, we can keep them mostly the same; differences are some of the namespace stuff and a couple of EXECUTORCH NOTEs.
ghstack-source-id: 284080528
@exported-using-ghexport

Differential Revision: [D74702689](https://our.internmc.facebook.com/intern/diff/D74702689/)

Author: swolchok

kernels/optimized/CMakeLists.txt

@@ -42,6 +42,7 @@ endif()
 # Build cpublas.
 list(TRANSFORM _optimized_cpublas__srcs PREPEND "${EXECUTORCH_ROOT}/")
 add_library(cpublas STATIC ${_optimized_cpublas__srcs})
+target_include_directories(cpublas PRIVATE ${TORCH_INCLUDE_DIRS})
 target_link_libraries(
   cpublas PUBLIC executorch_core eigen_blas extension_threadpool
 )