Merge pull request #29206 from kirtijindal14:doc_optimizations_v3

OpenCV New Documentation #29206

This PR introduces end to end working new Documentation in OpenCV.

Co-authored by: @abhishek-gola @omrope79 @Akansha-977 @Prasadayus @varun-jaiswal17 
### 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

modules/java/jar/CMakeLists.txt

@@ -87,7 +87,15 @@ install(FILES ${OPENCV_JAR_FILE} OPTIONAL DESTINATION ${OPENCV_JAR_INSTALL_PATH}
 
 add_dependencies(${the_module} ${the_module}_jar)
 
-if(BUILD_DOCS)
+# Javadoc generation can be disabled independently of BUILD_DOCS so the C++
+# Doxygen / Sphinx docs still build when the Java bindings carry Doxygen-style
+# tags (e.g. @retval, @remarks) that JDK doclint rejects as fatal errors.
+# Default ON for parity with upstream; when OFF the `doxygen_javadoc` target is
+# never created and doc/CMakeLists.txt's `if(TARGET doxygen_javadoc)` guard
+# drops it from the doxygen_cpp dependency chain automatically.
+option(BUILD_JAVADOC "Generate Javadoc as part of the documentation build" ON)
+
+if(BUILD_DOCS AND BUILD_JAVADOC)
   if(OPENCV_JAVA_SDK_BUILD_TYPE STREQUAL "ANT")
     add_custom_command(OUTPUT "${OPENCV_DEPHELPER}/${the_module}doc"
       COMMAND ${ANT_EXECUTABLE} -noinput -k javadoc