The optimization is for CV_8UC1 format and 3x3 box filter,
it is 15%~87% faster than current ocl kernel with below perf test

./modules/ts/misc/run.py -t imgproc --gtest_filter=OCL_BlurFixture*

Also add test cases for this ocl kernel.
Signed-off-by: Li Peng <peng.li@intel.com>

Fix findContours crash for very large images (#7451)

* Cast step to size_t in order to avoid integer overflow when processing very large images

* Change assert to CV_Assert

  * add performance test for 32F and 64F threshold
  * requires update of opencv_extra

  * add v_abs for universal intrinsic
  * add test of v_abs in test_intrin
  * fix compile error on gcc
  * fix bool OR operation

OpenCL Device:
- Intel(R) HD Graphics (OpenCL 2.0: r2.0.54425)

reduce scope of "i" variable

LSD: Avoid re allocating the histogram for multiple calls of LineSegmentDetector::detect in ll_angle

This is useful when reusing the same instance of LineSegmentDetector for multiple images