backporting of commit 98d96f2c

New class BufferArea is used to hide complexity of buffers allocations and allow instrumentation with valgrind and sanitizers.

CMakeLists.txt includes samples_utils.cmake, so the later should be
installed as well to make samples build successfully

If applied, this commit will describe permission denied message in imwrite_ function when user does not have write permission

* fixed antialiased line rendering to process image border correctly

* fixed warning on Windows

* imgproc(test): circle drawing regression

* fixed issue with Mat reshape in decodeMulti()

* added test for decodeMulti

* used assign

* Update py_thresholding.markdown

* 📝 Update py_thresholding.markdown

* added note about BORDER_TYPE in separable filters; fixed SGBMStereo description

* added # to BORDER_ constants to generate hyperlinks