aem: improve consistency of descriptor related #define constants
aem: improve consistency of descriptor related #define constants

- renamed entity_entity_id field to entity_id in entity descriptor
- add '_unit' suffix to all instances of audio_unit, video_unit and sensor_unit when missing
- renamed all backup_talker_unique_X fields to backup_talker_unique_id_X in stream descriptor
- add the 'signal_' prefix to all instances of signal_transcoder

jdkoftinoff/jdksavdecc-c,jdkoftinoff/jdksavdecc-mcu,arvidtp/jdksavdecc-c,jdkoftinoff/jdksavdecc-c,arvidtp/jdksavdecc-c,jdkoftinoff/jdksavdecc-c,jdkoftinoff/jdksavdecc-mcu,jdkoftinoff/jdksavdecc-c,jdkoftinoff/jdksavdecc-mcu,arvidtp/jdksavdecc-c,jdkoftinoff/jdksavdecc-mcu,arvidtp/jdksavdecc-c