Merge pull request #23596 from vrabaud:libavif

Add AVIF support through libavif. #23596

This is to fix https://github.com/opencv/opencv/issues/19271
Extra: https://github.com/opencv/opencv_extra/pull/1069

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

cmake/OpenCVFindLibsGrfmt.cmake

@@ -37,6 +37,16 @@ if(NOT ZLIB_FOUND)
   ocv_parse_header2(ZLIB "${${ZLIB_LIBRARY}_SOURCE_DIR}/zlib.h" ZLIB_VERSION)
 endif()
 
+# --- libavif (optional) ---
+
+if(WITH_AVIF)
+  ocv_clear_internal_cache_vars(AVIF_LIBRARY AVIF_INCLUDE_DIR)
+  include(cmake/OpenCVFindAVIF.cmake)
+  if(AVIF_FOUND)
+    set(HAVE_AVIF 1)
+  endif()
+endif()
+
 # --- libjpeg (optional) ---
 if(WITH_JPEG)
   if(BUILD_JPEG)