G-API: replace GAPI_Assert() with 'false' and '0' to GAPI_Error()
* gapi: GAPI_Error() macro
* gapi: replace GAPI_Assert() with 'false' and '0' to GAPI_Error()
* build: eliminate 'unreachable code' after CV_Error() (MSVC 2015)
* build: eliminate 'unreachable code' warning for MSVS 2015/2017
- observed in constructors stubs with throwing exception
G-API: add transformation logic to GCompiler
* Introduce transformation logic to GCOmpiler
* Remove partialOk() method
* Fix minor issues
* Refactor code according to code review
1. Re-design matchPatternToSubstitute logic
2. Update transformations order
3. Replace check_transformations pass with a
one time check in GCompiler ctor
* Revert unused nodes handling in pattern matching
* Address minor code review issues
* Address code review comments:
1) Fix some mistakes
2) Add new tests for endless loops
3) Update GCompiler's transformations logic
* Simplify GCompiler check for endless loops
1. Simplify transformations endless loops check:
- Original idea wasn't a full solution
- Need to develop a good method (heuristic?) to find loops
in general case (TODO)
2. Remove irrelevant Endless Loops tests
3. Add new "bad arg" tests and unit tests
* Update comments
