Merge pull request #18196 from mpashchenkov:mp/garray-initialization

[G-API]: Add GArray initialization support

* Added GArray initialization (CONST_VALUE, GScalar analog) and test for this

* Whitespaces

* And one more space

* Trailing whitespace

* Test name changed. Build with magic commands.

* GArray works with rvalue initialization

* Code cleanup

* Ternary operator in the initialization list.

modules/gapi/include/opencv2/gapi/garray.hpp

@@ -80,6 +80,7 @@ namespace detail
 
     protected:
         GArrayU();                                // Default constructor
+        GArrayU(const detail::VectorRef& vref);   // Constant value constructor
         template<class> friend class cv::GArray;  //  (available to GArray<T> only)
 
         void setConstructFcn(ConstructVec &&cv);  // Store T-aware constructor
@@ -328,6 +329,14 @@ namespace detail
 template<typename T> class GArray
 {
 public:
+    // Host type (or Flat type) - the type this GArray is actually
+    // specified to.
+    using HT = typename detail::flatten_g<typename std::decay<T>::type>::type;
+
+    explicit GArray(const std::vector<HT>& v) // Constant value constructor
+        : m_ref(detail::GArrayU(detail::VectorRef(v))) { putDetails(); }
+    explicit GArray(std::vector<HT>&& v)      // Move-constructor
+        : m_ref(detail::GArrayU(detail::VectorRef(std::move(v)))) { putDetails(); }
     GArray() { putDetails(); }             // Empty constructor
     explicit GArray(detail::GArrayU &&ref) // GArrayU-based constructor
         : m_ref(ref) { putDetails(); }     //   (used by GCall, not for users)
@@ -335,10 +344,6 @@ public:
     detail::GArrayU strip() const { return m_ref; }
 
 private:
-    // Host type (or Flat type) - the type this GArray is actually
-    // specified to.
-    using HT = typename detail::flatten_g<typename std::decay<T>::type>::type;
-
     static void VCTor(detail::VectorRef& vref) {
         vref.reset<HT>();
         vref.storeKind<HT>();