* models and data for layer norm

* add layer norm expanded model & data

* add code for generating models & data of layer norm expanded; add model & data for layer norm expanded with initializers

* reduce code

* remove optional output Mean & InvStdDev

Onnx conformance tests

* Add ONNX conformance tests

* dnn(onnx): make conformance stubs a part of repository
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>