* 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

backport of commit: 59b0314a

backport of commit: f18cbd03

This fixes a compiler error on MSVC with Unreal Engine (at least).

backport of commit: 4e998c9a

backport of commit: 95c65aff

OpenCv.js docker container build instructions (#15221)

* emscripten docker container

* docker

* typo

* typo

* whitespace issue

Fix build for UWP (#15207)

* Guard non-WinRT calls to fix UWP build

* Remove unnecessary guard for WinRT

G-API: verify y offset and height of Fluid output ROIs (#15190)

* G-API: validate GFluidOutputRoi y and height

* Rearrange tested ROIs