[GSoC] Add GIF decode and encode for imgcodecs #25691
this is related to #24855
we add gif support for `imread`, `imreadmulti`, `imwrite` and `imwritemulti`
opencv_extra: https://github.com/opencv/opencv_extra/pull/1203
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Missing include directories needed for wayland-util and xkbcommon #26563
See: #26561
### Pull Request Readiness Checklist
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Emscripten build fixes#26537
- Corrects typo in Emscripten-only intrinsics header (Fixes https://github.com/opencv/opencv/issues/26536)
- Updates deprecated intrinsic title (as per LLVM final intrinsic name).
### Pull Request Readiness Checklist
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HAL added for absdiff(array, scalar) + related fixes#26459
### This PR changes
* HAL for `absdiff` when one of arguments is a scalar, including multichannel arrays and scalars
* several channels support for HAL `addScalar`
* proper data type check for `addScalar` when one of arguments is a scalar
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The new C++ code is copy/pasted from OpenCV5:
- functions initIntrinsicParams2D, subMatrix (the first 160 lines)
- function prepareDistCoeffs
- the different asserts
Not all the API/code is ported to C++ yet to ease the review.
HAL added for add(array, scalar) #25624
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int64 data type support for FileStorage. 1d and empty Mat with exact dimensions #26434
### Pull Request Readiness Checklist
Port of https://github.com/opencv/opencv/pull/26399 to 4.x branch
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Backport C++ stereo/stereo_geom.cpp:5.x to calib3d/stereo_geom.cpp:4.x #26437
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