[Core] Refactor activation and normalization layers (#5493)
* move out the activations.
* move normalization layers.
* add doc.
* add doc.
* fix: paths
* Apply suggestions from code review
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
* style
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Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
