Merge remote-tracking branch 'upstream/3.4' into merge-3.4

diff --cc modules/calib3d/src/circlesgrid.cpp
Simple merge

diff --cc modules/core/include/opencv2/core/types.hpp
Simple merge

diff --cc modules/core/test/test_mat.cpp
Simple merge

diff --cc modules/imgproc/src/drawing.cpp
Simple merge

diff --cc modules/ml/src/ann_mlp.cpp
Simple merge

diff --cc modules/ts/include/opencv2/ts/ts_perf.hpp
Simple merge

diff --cc modules/videoio/src/cap_v4l.cpp
Simple merge

diff --cc modules/videoio/src/videoio_registry.cpp
index f3e7ec581d7ff68b723f2be4ec1a4ce43b0d4df3,85fc239ad954d384947428b34eb0b40406c0e4c5..e3d0bcab951787eb9309d5d959d5bd075a70b236
--- 1/modules/videoio/src/videoio_registry.cpp
--- 2/modules/videoio/src/videoio_registry.cpp
+++ b/modules/videoio/src/videoio_registry.cpp
@@@ -6,8 -6,9 +6,10 @@@
  
  #include "videoio_registry.hpp"
  
+ #include "opencv2/videoio/registry.hpp"
+ 
  #include "cap_intelperc.hpp"
 +#include "cap_librealsense.hpp"
  #include "cap_dshow.hpp"
  
  #ifdef HAVE_MFX