cpu: move all the operators into a separate c++ file (except mul_mat) (ggml/1167)

cpu: move all the operators into a separate c++ file (except mul_mat) (ggml/1167)

* cpu: refactor SIMD mappings and vectorized op functions into separate files

* Fix warning for ggml_float to float

* Fix warnings

* cpu: move all the operations (except mul_mat) to a separate c++ file

* fix whitespace

* Update ggml/src/ggml-cpu/vec.h

Co-authored-by: Diego Devesa <redacted>
* Fix PR comments - use GGML_UNUSED, use cassert in ops.cpp

* Reverse the order of import for ops.h and vec.h, to match what was present in ggml-cpu.c previously

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Co-authored-by: Diego Devesa <redacted>