* Unit tests for MatMulInteger

* Add ONNX MatMulInteger op

* Add QuantizedLinearMatmulInteger builder

* Additional unit test

* Exclude tests on nVidia GPU backend

* Add 4D test case

* Enable >2D MatMulInteger

* Refactoring to MatMulFactory - step 1

* Refactoring to MatMulFactory - step 2

* Remove `using namespace ngraph` to make `Node` unambiguous.

* Disable quantized ops tests on GPU backend

* Remove unused `includes`

* Remove redundant dynamic_pointer_cast

* Remove redundant `move`

* Add const correctness

* Code review comments

* Style apply

* Add documentation

* Use more complex shapes in tests