Group 5G platform types for common 5G-specific types

common/5g_platform_types.h

common/ngran_types.h

openair2/COMMON/e1ap_messages_types.h

openair2/COMMON/f1ap_messages_types.h

openair2/COMMON/ngap_messages_types.h

openair2/E1AP/e1ap.c

openair2/F1AP/f1ap_cu_ue_context_management.c

openair2/F1AP/f1ap_du_ue_context_management.c

openair2/LAYER2/NR_MAC_gNB/mac_rrc_dl_handler.c

openair2/RRC/NR/rrc_gNB.c

openair2/RRC/NR/rrc_gNB_NGAP.c