Merge pull request #16118 from smirnov-alexey:as/gopaque

G-API: GOpaque implementation

* Stub initial copypasted solution

* Fix mov test and add a couple of others

* Fix warnings

* More code coverage and tests

* fix macos warning

* address review comments

* Address review comments and fix indentation

* Fix build on armv7

modules/gapi/src/compiler/gcompiler.cpp

@@ -332,6 +332,9 @@ void cv::gimpl::GCompiler::validateInputMeta()
         case GProtoArg::index_of<cv::detail::GArrayU>():
             return util::holds_alternative<cv::GArrayDesc>(meta);
 
+        case GProtoArg::index_of<cv::detail::GOpaqueU>():
+            return util::holds_alternative<cv::GOpaqueDesc>(meta);
+
         default:
             GAPI_Assert(false);
         }

modules/gapi/src/compiler/gobjref.hpp

@@ -16,13 +16,14 @@ namespace cv
 
 namespace gimpl
 {
-    // Union type for various user-defined type constructors (GArray<T>, etc)
+    // Union type for various user-defined type constructors (GArray<T>, GOpaque<T>, etc)
     // FIXME: Replace construct-only API with a more generic one
     //    (probably with bits of introspection)
     // Not required for non-user-defined types (GMat, GScalar, etc)
     using HostCtor = util::variant
     < util::monostate
     , detail::ConstructVec
+    , detail::ConstructOpaque
     >;
 
     using ConstVal = util::variant

modules/gapi/src/compiler/passes/dump_dot.cpp

@@ -32,6 +32,7 @@ void dumpDot(const ade::Graph &g, std::ostream& os)
         {cv::GShape::GMAT,    "GMat"},
         {cv::GShape::GSCALAR, "GScalar"},
         {cv::GShape::GARRAY,  "GArray"},
+        {cv::GShape::GOPAQUE, "GOpaque"},
     };
 
     auto format_op_label  = [&gr](ade::NodeHandle nh) -> std::string {