Update miniflann.cpp

Update test_stereomatching.cpp

size_t is not supported cv::Mat type

Remove unnecessary Non-ASCII characters from source code (#9075)

* Remove unnecessary Non-ASCII characters from source code

Remove unnecessary Non-ASCII characters and replace them with ASCII
characters

* Remove dashes in the @param statement

Remove dashes and place single space in the @param statement to keep
coding style

* misc: more fixes for non-ASCII symbols

* misc: fix non-ASCII symbol in CMake file

Add missing sstream header for decl of std::ostringstream in line 104

std::rand() has no thread-safe guarantee.

Adding of destructor and placement new constructors for classes wrapped with CV_EXPORTS_W_SIMPLE macro

cosmetic changes to fix this warning.
real bugs not found

(cherry picked from commit 408107ce)

(cherry picked from commit 3934d61d)

(cherry picked from commit 32d7c195)

Backport of mariusmuja/flann@f8ca6df3.

Backport of mariusmuja/flann@f8ca6df3.

Conflicts:
	modules/contrib/include/opencv2/contrib/retina.hpp

Current implementation of miniflann is releasing the trained index, and
rebuilding the index from the beginning.
But, some indexing algorithms like the LSH are able to add the indexing
data after that.
This branch is implementation of that optimization for LshIndex
FlannBasedMatcher in the feature2d.

(cherry picked from commit 8910508b)