* G-API: rename ArgKind OPAQUE to GOPAQUE

Rename ArgKind value to GOPAQUE to fix conflict in the
user code when wingdi.h is included: it defines OPAQUE
macro that (for some reason) is chosen instead of ArgKind
value

* Add compatibility with existing API

* Renamed GOPAQUE to OPAQUE_VAL

* Determine input shapes

* Add test

* Remove getInputShapes

* Fix model

* Fix constructors

* Add Caffe test

* Fix predict

* 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

- addresses #15163: C++11 definition issue by @neheb

Fix build for UWP (#15207)

* Guard non-WinRT calls to fix UWP build

* Remove unnecessary guard for WinRT