[Fix, Test] (MG_Backend/DirectVulkan, MG_IntegrationTest): map a layered CopyImageSubData onto the axis each endpoint keeps its slices on, instead of copying slice 0 and calling it done

MobileGL/MG_IntegrationTest/CMakeLists.txt

@@ -79,6 +79,7 @@ add_executable(MobileGLIntegrationTest
     Scenarios/XfbCaptureBufferReuseScenario.cpp
     Scenarios/VertexArrayEnableDisableScenario.cpp
     Scenarios/CopyImageLevelRangeScenario.cpp
+    Scenarios/CopyImageLayeredScenario.cpp
 )
 
 target_include_directories(MobileGLIntegrationTest PRIVATE