Initial separation of enc/dec functions from handlers/callbacks

* move enc/dec definitions to NR_NAS_defs.h and add new lib file nr_fgs_nas_lib.c
  both used by nr_nas_msg.c
* move utility macros to fgs_nas_utils.h: this can be used in all the 5GMM, 5GSM lib files
* use nr_nas_msg.c for handlers/callbacks only, it should call the enc/dec
  functions in nr_fgs_nas_lib and in the 5GMM, 5GSM libs
* 5GMM, 5GSM libs should only do the enc/dec of the NAS message contents

openair3/NAS/COMMON/IES/CMakeLists.txt

@@ -3,6 +3,4 @@ add_library(nas_common_ies_lib OBJECT
     NasKeySetIdentifier.c
 )
 
-target_include_directories(nas_common_ies_lib PRIVATE
-    ${CMAKE_CURRENT_SOURCE_DIR}
-)
+target_include_directories(nas_common_ies_lib PUBLIC .)