Qt6 compatibility (#968)

* Qt6 Compilation success

* Fixed qt5 backward compatibility

* Fixed build for qt<=5.9 (bionic)

* Added docker file for easy testing with latest Qt/VTK/PCL/OpenCV

* Fixed cmake for qt

docker/latest_deps/Dockerfile

@@ -0,0 +1,63 @@
+
+FROM osrf/ros:humble-desktop
+
+# Install build dependencies
+RUN apt-get update && \
+    apt-get install -y git software-properties-common ros-humble-rtabmap-ros libqt6* qt6* && \
+    apt-get remove -y ros-humble-rtabmap libpcl* libqt5* qt5* libvtk* libopencv* && \
+    apt-get clean && rm -rf /var/lib/apt/lists/
+
+WORKDIR /root/
+
+RUN rm /bin/sh && ln -s /bin/bash /bin/sh
+
+# ros2 seems not sourcing by default its multi-arch folders
+ENV LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/ros/humble/lib/x86_64-linux-gnu
+
+# Build latest VTK with Qt6
+RUN git clone https://github.com/Kitware/VTK.git && \
+    cd VTK && \
+    mkdir build && \
+    cd build && \
+    cmake -DVTK_GROUP_ENABLE_Qt=YES .. && \
+    make -j$(nproc) && \
+    make install && \
+    cd ../.. && \
+    rm -rf VTK
+    
+# Build latest PCL with latest VTK
+RUN git clone https://github.com/PointCloudLibrary/pcl.git && \
+    cd pcl && \
+    mkdir build && \
+    cd build && \
+    cmake -DBUILD_tools=OFF .. && \
+    make -j$(nproc) && \
+    make install && \
+    cd ../.. && \
+    rm -rf pcl
+    
+# Build latest OpenCV
+RUN git clone https://github.com/opencv/opencv.git && \
+    git clone https://github.com/opencv/opencv_contrib.git && \
+    cd opencv && \
+    mkdir build && \
+    cd build && \
+    cmake -DBUILD_opencv_python3=OFF -DBUILD_opencv_python_bindings_generator=OFF -DBUILD_opencv_python_tests=OFF -DBUILD_PERF_TESTS=OFF -DBUILD_TESTS=OFF -DOPENCV_EXTRA_MODULES_PATH=/root/opencv_contrib/modules .. && \
+    make -j$(nproc) && \
+    make install && \
+    cd ../.. && \
+    rm -rf opencv
+
+# Copy current source code
+COPY . /root/rtabmap
+
+# Build RTAB-Map project
+RUN source /ros_entrypoint.sh && \
+    cd rtabmap/build && \
+    cmake .. && \
+    make -j$(nproc) && \
+    make install && \
+    cd ../.. && \
+    rm -rf rtabmap && \
+    ldconfig
+