- backport 15290
- add extra test case

* imgproc: fix bit-exact GaussianBlur() / sepFilter2D()

- avoid kernels with bad approximation
- GaussiabBlur - apply error-diffusion approximation for kernel (8-bit fraction)

* java(test): update features2d ref data

* test: update test_facedetect

Js test puppeteer

* run_puppeteer.js / tests

* js run test section

* rollback html

* whitespace

* js: update OpenCV.js tests infrastructure

* js: exclude puppeteer from default 'npm install'

* js: update notes

* js: more fixes in run_puppeteer

* fix build folder

JS - adds a tutorial about running opencv.js in Node.js

Implement GArik's comments

Remove unnecessary c_str()

Fix brace position

Supported ONNX Squeeze, ReduceL2 and Eltwise::DIV

* Support eltwise div

* Fix test

* OpenCL support added

* refactoring

* fix code style

* Only squeeze with axes supported

Fix an error during Windows installation caused by trying to create the already existing Build directory. Also excluding intermediate steps for Install directory creation.

* Grammar fixes for python core operations docs

* fixed whitespace error

* reverted changes

Signed-off-by: SSE4 <tomskside@gmail.com>