[G-API]: countNonZero() Standard Kernel Implementation
* Add countNonZero() standard kernel
- API and documentation provided
- OCV backend supported
- accuracy and performance tests provided
- some refactoring of related documentation done
* Fix GOpaque functionality for OCL Backend
- test for OCL Opaque usage providied
* countNonZero for GPU
- OCL Backend implementation for countNonZero() added
- tests provided
* Addressing comments
[G-API]: Add Fluid bitwise operations implementation for (GMat, GScalar)
* Added Fluid `bitwise` with `Scalar` + acc.tests
- simple loop implementation for Fluid used (no `hal`);
- `Scalar` is casted to `int` in the beginning
- tests just modified to work with `Scalar`
- expected output in operators' tests fixed (operators can't change Mat's depth)
- `float` `Scalar` `RNG` added, `RNG` reworked (`time` is used now), initialization of test fixtures reworked
- if input or output is `float` Scalar is initialized by `float`
- some problems with Fluid/OCV floating-point comparison difference stashed by `AbsSimilarPoints()` usage, FIXME added
- divide-by-zero is now fixed differently and everywhere
* - Added perf_tests for bitwise_Scalar operations
- due to errors of Fluid floating-point comparison operations, added support of different validation in Cmp perf_tests; added FIXME
- reworked integral initialization of Scalar
* Addressing comments
- NULL -> nullptr
- Scalar convertion moved to the function
- avoid -> avoiding
* Addressing comments
* CV_assert -> GAPI_assert
* Addressed DM comments
- refactored convertScalarForBitwise()
- removed unnecessary braces for switch
* Changed the operators tests
- switch via `enum` implemented
- infrastructure for that refactored
G-API: Laplacian and bilateralFilter standard kernels
* Added Laplacian kernel and tests
* Added: Laplacian kernel, Bilateral kernel (CPU, GPU); Performance and accuracy tests for this kernels
* Changed tolerance for GPU test
* boner
* Some changes with alignment; Tests's parameters are the same as for OCV
* Cut tests
* Compressed tests
* Minor changes (rsrt bb)
* Returned types
More fixes for G-API tests (#13251)
* scalar comparator and more fixes for tests
* add weighted aligned
* white space
* more white space
* Add weighted test accuracy check enabled
G-API GPU-OpenCL backend (#13008)
* gpu/ocl backend core
* accuracy tests added and adjusted + license headers
* GPU perf. tests added; almost all adjusted to pass
* all tests adjusted and passed - ready for pull request
* missing license headers
* fix warning (workaround RGB2Gray)
* fix c++ magic
* precompiled header
* white spaces
* try to fix warning and blur test
* try to fix Blur perf tests
* more alignments with the latest cpu backend
* more gapi tests refactoring + 1 more UB issue fix + more informative tolerance exceed reports
* white space fix
* try workaround for SumTest
* GAPI_EXPORTS instead CV_EXPORTS
