Conditionally use cmake_path on cmake < 3.20 (#424)

Signed-off-by: Michael Carroll <mjcarroll@intrinsic.ai>

Author: Michael Carroll

gz-msgs-extras.cmake.in

@@ -22,7 +22,15 @@ include(${@PROJECT_NAME@_DIR}/gz_msgs_factory.cmake)
 include(${@PROJECT_NAME@_DIR}/gz_msgs_generate.cmake)
 
 set(@PROJECT_NAME@_INSTALL_PATH "${@PROJECT_NAME@_DIR}/@PROJECT_CMAKE_EXTRAS_PATH_TO_PREFIX@")
-cmake_path(NORMAL_PATH @PROJECT_NAME@_INSTALL_PATH OUTPUT_VARIABLE @PROJECT_NAME@_INSTALL_PATH)
+
+if(CMAKE_VERSION VERSION_LESS "3.20.0") 
+  file(TO_CMAKE_PATH @PROJECT_NAME@_INSTALL_PATH NORMALIZED_PATH)  # Converts native path to CMake style with forward slashes.
+  get_filename_component(ABSOLUTE_PATH "${NORMALIZED_PATH}" ABSOLUTE)  # Extracts the absolute path component.
+  set(@PROJECT_NAME@_INSTALL_PATH "${ABSOLUTE_PATH}")  # Stores the normalized absolute path back to the original variable.
+else()
+  cmake_path(NORMAL_PATH @PROJECT_NAME@_INSTALL_PATH OUTPUT_VARIABLE @PROJECT_NAME@_INSTALL_PATH)
+endif()
+
 set(PROTOC_NAME "$<TARGET_FILE_NAME:@PROJECT_NAME@_protoc_plugin>")
 set(PROTO_SCRIPT_NAME "@PROJECT_NAME@_generate.py")
 set(FACTORY_SCRIPT_NAME "@PROJECT_NAME@_generate_factory.py")
@@ -37,7 +45,7 @@ if(NOT DEFINED @PROJECT_NAME@_PROTOC_EXECUTABLE)
 endif()
 if(NOT DEFINED @PROJECT_NAME@_PYTHON_INTERPRETER)
   set(@PROJECT_NAME@_PYTHON_INTERPRETER Python3::Interpreter)
-endif() 
+endif()
 set(@PROJECT_NAME@_PROTO_GENERATOR_SCRIPT ${@PROJECT_NAME@_INSTALL_PATH}/bin/${PROTO_SCRIPT_NAME})
 set(@PROJECT_NAME@_FACTORY_GENERATOR_SCRIPT ${@PROJECT_NAME@_INSTALL_PATH}/bin/${FACTORY_SCRIPT_NAME})