C-API cleanup: apps, imgproc_c and some constants #25075
Merge with https://github.com/opencv/opencv_contrib/pull/3642
* Removed obsolete apps - traincascade and createsamples (please use older OpenCV versions if you need them). These apps relied heavily on C-API
* removed all mentions of imgproc C-API headers (imgproc_c.h, types_c.h) - they were empty, included core C-API headers
* replaced usage of several C constants with C++ ones (error codes, norm modes, RNG modes, PCA modes, ...) - most part of this PR (split into two parts - all modules and calib+3d - for easier backporting)
* removed imgproc C-API headers (as separate commit, so that other changes could be backported to 4.x)
Most of these changes can be backported to 4.x.
Merge two Haar Cascade tutorials (#14674)
* move haar cascade introduction, add code explanation, mark content as moved
* switch to ref for include to provide correct breadcrumb navigation
corrected constants, changed objdetection.cpp as well
updated objDetection2.cpp as well
fixed headers in objdetection2.cpp
removed useles RNG
fixed buildbot warnings (wow, i like that bot!)
victim of the war on whitespace
fixing buildbot warnings
fixing last buildbot warning, heya .
trying to rebase/squash commits