Revamp nav2_behavior_tree CMakeLists.txt to use modern idioms.#4485

SteveMacenski merged 1 commit intoros-navigation:mainros-navigation/navigation2:mainfrom

clalancette:clalancette/main-nav2-behavior-treeclalancette/navigation2:clalancette/main-nav2-behavior-treeCopy head branch name to clipboard