G-API: GAPI_TRANSFORM internal functionality rework (#14952)
* Change internal pattern and substitute signatures and refactor tests
* Enhance GArrayU with type-checker function
Add a couple of new tests on GAPI_TRANSFORM
* Introduce GAPI_TRANSFORM initial interface
Comes along with simple tests and kernel package changes
* Fix documentation and adjust combine() function
* Fix stuff after rebasing on master
* Remove redundant functionality
* Refactoring according to review feedback provided
* Fixes according to review feedback
* Reconsider transformations return and fix a warning
* Fixes from code review
* Add a new simple test
* Cleanup, added tests on GScalar, GMatP, GArray
smirnov-alexey