Merge pull request #20039 from sivanov-work:gapi_empty_input

G-API: Implement variant visit()

* Add variant visitor, use visitor for check compile args

* Fix GAPI UT: variant *compiler

* Aling apply_visior with std, fix indentations

* Fix compilation (included compiler_hints.hpp)

* Fix compilation (due gapi standalone)

* Fix compilation2 (Docs)

* Add Lambdas overload, Refactor visit()

* Add ReturnType auto deduction

* Fix comilation

* Fix compilation

* Fix warnings

* Try to fix MSVC14

* Fix docs

* Try fix Win compile

* Fix Docs again

* Revert GAPI empty input fix

* Apply comment for `tuple_element`

* Add std::decay for std::base_of to work arounf armv7 problem

* Apply review comments

* Apply review comments: added comment & removed unused args

* Fix docs compilation

modules/gapi/src/api/gproto.cpp

@@ -14,7 +14,6 @@
 
 #include "api/gorigin.hpp"
 #include "api/gproto_priv.hpp"
-#include "logger.hpp"
 
 // FIXME: it should be a visitor!
 // FIXME: Reimplement with traits?
@@ -277,13 +276,9 @@ void cv::validate_input_arg(const GRunArg& arg)
 
 void cv::validate_input_args(const GRunArgs& args)
 {
-    GAPI_LOG_DEBUG(nullptr, "Total count: " << args.size());
-    size_t index = 0;
     for (const auto& arg : args)
     {
-        GAPI_LOG_DEBUG(nullptr, "Process index: " << index);
         validate_input_arg(arg);
-        index ++;
     }
 }