core: rework code locality

- to reduce binaries size of FFmpeg Windows wrapper
- MinGW linker doesn't support -ffunction-sections (used for FFmpeg Windows wrapper)
- move code to improve locality with its used dependencies
- move UMat::dot() to matmul.dispatch.cpp (Mat::dot() is already there)
- move UMat::inv() to lapack.cpp
- move UMat::mul() to arithm.cpp
- move UMat:eye() to matrix_operations.cpp (near setIdentity() implementation)
- move normalize(): convert_scale.cpp => norm.cpp
- move convertAndUnrollScalar(): arithm.cpp => copy.cpp
- move scalarToRawData(): array.cpp => copy.cpp
- move transpose(): matrix_operations.cpp => matrix_transform.cpp
- move flip(), rotate(): copy.cpp => matrix_transform.cpp (rotate90 uses flip and transpose)
- add 'OPENCV_CORE_EXCLUDE_C_API' CMake variable to exclude compilation of C-API functions from the core module
- matrix_wrap.cpp: add compile-time checks for CUDA/OpenGL calls
- the steps above allow to reduce FFmpeg wrapper size for ~1.5Mb (initial size of OpenCV part is about 3Mb)

backport is done to improve merge experience (less conflicts)
backport of commit: 65eb946756

modules/core/src/dxt.cpp

@@ -4640,6 +4640,9 @@ int cv::getOptimalDFTSize( int size0 )
     return optimalDFTSizeTab[b];
 }
 
+
+#ifndef OPENCV_EXCLUDE_C_API
+
 CV_IMPL void
 cvDFT( const CvArr* srcarr, CvArr* dstarr, int flags, int nonzero_rows )
 {
@@ -4695,4 +4698,5 @@ cvGetOptimalDFTSize( int size0 )
     return cv::getOptimalDFTSize(size0);
 }
 
+#endif  // OPENCV_EXCLUDE_C_API
 /* End of file. */