Optimize exposure compensation (#13400)

* Added perf test

* Optimized gains computation

* Use Eigen for gains calculation

RGB to/from Gray rewritten to wide intrinsics (#13379)

* 5x5 to RGB added

* RGB25x5 added

* Gray2RGB added

* Gray2RGB5x5 added

* vx_set moved out of loops

* RGB5x52Gray added

* RGB2Gray written

* warnings fixed (int -> (u)short conversion)

* warning fixed

* warning fixed

* "i < n-vsize+1" to "i <= n-vsize"

* RGBA2mRGBA vectorized

* try to fix ARM builds

* fixed ARM build for RGB2RGB5x5

* mRGBA2RGBA: saturation, vectorization

* fixed CL implementation of mRGBA2RGBA (saturation added)

Replaced CV_TM_SQDIFF to TM_SQDIFF and the rest since methods are renamed in opencv 3.4

* added performance test for compareHist

* compareHist reworked to use wide universal intrinsics

* Disabled vectorization for CV_COMP_CORREL and CV_COMP_BHATTACHARYYA if f64 is unsupported

Add ability to build iOS and macOS frameworks with nonfree modules (#13424)

* Allow building ios framework with nonfree

* Allow building osx framework with nonfree

On windows 7, MinCore_Downlevel does not work correctly. However, the only API used was QISearch, which can be found in Shlwapi.

Closes #12010

* try to solve #13381

* Add note

* Added dependency verification mechanism for cmake

moved to CMakeFiles (no conflicts are expected)

DNN backends registry (#13332)

* Added dnn backends registry

* dnn: process DLIE/FPGA target