Fix gradients canny cht

[rolalaro]

• Choice between the OpenCV and ViSP backend for the Canny computation
• Computation of the gradient using Gaussian blur + Sobel instead of derivativeGaussianFillter
• New method of Canny auto threshold

[codecov]

Codecov Report

Attention: 375 lines in your changes are missing coverage. Please review.

Comparison is base (fe4e89c) 54.75% compared to head (2512b21) 54.37%.
Report is 16 commits behind head on master.

❗ Current head 2512b21 differs from pull request most recent head ae3f1ad. Consider uploading reports for the commit ae3f1ad to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1249      +/-   ##
==========================================
- Coverage   54.75%   54.37%   -0.38%     
==========================================
  Files         403      403              
  Lines       50261    50507     +246     
==========================================
- Hits        27519    27464      -55     
- Misses      22742    23043     +301     

Files	Coverage Δ
modules/core/include/visp3/core/vpHistogram.h	25.00% <ø> (ø)
modules/core/include/visp3/core/vpImageConvert.h	93.33% <ø> (ø)
modules/imgproc/src/vpImgproc.cpp	92.85% <100.00%> (-0.38%)	⬇️
modules/core/src/tools/histogram/vpHistogram.cpp	78.66% <93.33%> (+0.73%)	⬆️
...les/core/include/visp3/core/vpCannyEdgeDetection.h	0.00% <0.00%> (ø)
modules/core/src/image/vpImageConvert.cpp	18.47% <0.00%> (-0.19%)	⬇️
...roc/include/visp3/imgproc/vpCircleHoughTransform.h	0.00% <0.00%> (ø)
modules/imgproc/src/vpCircleHoughTransform.cpp	0.00% <0.00%> (ø)
modules/core/src/image/vpCannyEdgeDetection.cpp	0.00% <0.00%> (ø)
modules/core/include/visp3/core/vpImageFilter.h	68.92% <26.08%> (-23.51%)	⬇️
... and 1 more

... and 28 files with indirect coverage changes

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[rolalaro]

Remaining work:

• Add a tutorial for Canny
• Add a method to compute the partial normalized gradients
• If auto keyword is not allowed, change the scaleFilter lambda into a method in vpImageFilter (?)