Merge pull request #15090 from dmatveev:dm/ng-0001-g-api-inference-api

* G-API-NG/API: Introduced inference API and IE-based backend

- Very quick-n-dirty implementation
- OpenCV's own DNN module is not used
- No tests so far

* G-API-NG/IE: Refined IE backend, added more tests

* G-API-NG/IE: Fixed various CI warnings & build issues + tests

- Added tests on multi-dimensional own::Mat
- Added tests on GMatDesc with dimensions
- Documentation on infer.hpp
- Fixed more warnings + added a ROI list test
- Fix descr_of clash for vector<Mat> & standalone mode
- Fix build issue with gcc-4.8x
- Addressed review comments

* G-API-NG/IE: Addressed review comments

- Pass `false` to findDataFile()
- Add deprecation warning suppression macros for IE

modules/gapi/src/compiler/gmodel.cpp

@@ -47,7 +47,7 @@ ade::NodeHandle GModel::mkDataNode(GModel::Graph &g, const GOrigin& origin)
     {
         auto value = value_of(origin);
         meta       = descr_of(value);
-        storage    = Data::Storage::CONST;
+        storage    = Data::Storage::CONST_VAL;
         g.metadata(data_h).set(ConstValue{value});
     }
     g.metadata(data_h).set(Data{origin.shape, id, meta, origin.ctor, storage});