G-API: Tutorial: Face beautification algorithm implementation

* Introduce a tutorial on face beautification algorithm

- small typo issue in render_ocv.cpp

* Addressing comments rgarnov smirnov-alexey

* Support ARM64 Windows 10 platform

* Fixed detection issue for ARM64 Windows 10

* Try enabling ARM NEON intrin

* build: disable NEON with MSVC compiler

* samples(directx): gdi32 dependency

* (doc): added info about STAR

* (doc): fixed typos and sentence structure

* fixed trailing whitespaces

cuda4dnn: fuse activations with convolutions

* fuse ReLU, ReLU6, TanH, Sigmoid with conv

* fix OpenCL errors

* improve ReLU, add power, swish and mish

* fix missing fusion entries

* fix handling of unsetAttached

* remove whole file indentation

* optimize power = 1.0, use IDENTITY instead of NONE

* handle edge case: change backend and then clear

* Eltwise::DIV support in Halide backend

* fix typo

* remove div from generated test suite to pass CI, switching to manual test...

* ensure divisor not near to zero

* use randu

* dnn(test): update test data for Eltwise.Accuracy/DIV layer test

Keypoints module

* 3rdparty: update libwebp 1.0.2 => 1.0.3

https://github.com/webmproject/libwebp/releases/tag/v1.0.3

* 3rdparty(libwebp): re-apply patches

* cmake: avoid deprecated LINK_PRIVATE/LINK_PUBLIC

see CMP0023 (CMake 2.8.12+)

* cmake: fix 3rdparty list

- don't include OpenCV modules

Add checks for empty operands in Matrix expressions that don't check properly

* Starting to add checks for empty operands in Matrix expressions that
don't check properly.

* Adding checks and delcarations for checker functions

* Fix signatures and add checks for each class of Matrix Expr operation

* Make it catch the right exception

* Don't expose helper functions to public API

G-API: Mosaic handle corner cases

* Handle corner cases

* Fix mosaic algo

* Fix bug with empty rects

* G-API: Added G-API Overview slides & its source code

- Sample code snippets are moved to separate files;
- Introduced a separate benchmark to measure Fluid/OpenCV
  performance;
- Added notes on API changes (it is still a 4.0, not a 4.2 talk!)
- Added a "Metropolis" beamer download-n-build script.

* G-API: Addressed review issues on G-API overview slides

* imgproc: Prevent 1B overrun of 8C3 SIMD optimization

The fourth value read via v_load_q is essentially ignored,
but can cause trouble if it happens to cross page boundaries.

The final few iterations may attempt to read the most extreme
elements of S, which will read 1B beyond the array in most
aligment cases. Dynamically compute the stop. This could be
hoised from the loop, but will require a more extensive change.

Likewise, cleanup the iteration increment statements to make
it more obvious they do channel count (3) elements per pass.

This should resolve #16137

* imgproc(resize): extra check

dnn(eltwise): fix handling of different number of channels

* dnn(test): reproducer for Eltwise layer issue from PR16063

* dnn(eltwise): rework support for inputs with different channels

* dnn(eltwise): get rid of finalize(), variableChannels

* dnn(eltwise): update input sorting by number of channels

- do not swap inputs if number of channels are same after truncation

* dnn(test): skip "shortcut" with batch size 2 on MYRIAD targets