Revise LRN reference implementation (#2672)
* fix typo in LRN docs
* fix link to reference in LRN doc
* LRN, LRN_IE types alignment with spec
* align LRN ref implementation to plugins behavior
* update LRN docs
* Improve LRN reference implementation performance
* restore LRN constructor with no axes in the input
* apply code format
* revert double->float size_t->int change
* small fix to example in doc
* revert double->float size_t->int in onnx_importer and backend tests
* Changes to docs after review