Add ROS_ROOT configuration for cross-compilation

Add ROS_ROOT argument to compose.yaml, update toolchain CMake to search
in ROS_ROOT, and modify final stage of Dockerfiles to copy to ROS_ROOT
instead of TARGET_SYSROOT. Also add support for ROS2 lyrical distro.

cross_compile/compose.yaml

@@ -32,9 +32,11 @@ services:
     build:
       context: .
       dockerfile: ros2/${ROS_DISTRO}/ros_${ROS_DISTRO}.Dockerfile
+      # target: ros_builder
       args:
         ROS_DISTRO: ${ROS_DISTRO}
         PLATFORM: ${PLATFORM}
+        ROS_ROOT: /opt/ros/${ROS_DISTRO}
         CC_PLATFORM_IMAGE: ${PLATFORM}/cc-toolchain:latest
         VENDOR_PACKAGES_IMAGE: ${PLATFORM}/cc-vendor-packages:latest
     image: ${PLATFORM}/cc-ros-${ROS_DISTRO}:latest