Docs: Fix repeated 'the' typos in comments and documentation

[LOTUS9679]

Found and fixed multiple instances of the typo "the the" (repeated words) in documentation and code comments.

Files modified:

• TDS_2/include/CGAL/Triangulation_data_structure_2.h
• Shape_regularization/doc/Shape_regularization/Concepts/RegularizationType.h
• Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/distance.h
• Isosurfacing_3/examples/Isosurfacing_3/contouring_octree.cpp

[albert-github]

Strange I don't see any of these problems in the main branch of CGAL.

FYI I wrote a small script to detect the double words and are currently evaluating these and will make a proposed PR out of the results.

[LOTUS9679]

Thanks Albert! If you have a script to catch all occurrences globally, that is definitely the better approach. I will close this PR so it doesn't conflict with your work. Looking forward to seeing the cleanup!