* [SPEC] Add new v1::VariadicSplit operator

* Add missing namespace, fix a typo in doc

* Apply suggestions from code review
Co-Authored-By: Michał Karzyński <postrational@users.noreply.github.com>

* Style fix

* Set all of the inputs to be relevant to output shape

* Set output type if numer of outputs is known

* Add node validation for known input