G-API: clean up accuracy tests (#14945)

* Delete createOutputMatrices flag

Update the way compile args function is created

Fix instantiation suffix print function

* Update comment (NB)

* Make printable comparison functions

* Use defines instead of objects for compile args

* Remove custom printers, use operator<< overload

* Remove SAME_TYPE and use -1 instead

* Delete createOutputMatrices flag in new tests

* Fix GetParam() printed values

* Update Resize tests: use CompareF object

* Address code review feedback

* Add default cases for operator<< overloads

* change throw to GAPI_Assert

G-API: Align operators tests to new test model (#14922)

* Align operators tests to new test model

* Change init function in NotOperatorTest

G-API rename GPU backend to OCL backend (#13240)

* renaming draft

* inline namespace instead non-safe define

* more back compatibility

* Updates after review from Dmitry

avoid `countNonZero()`, use `norm()`

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