Rules like the mentioned are in the traffic code of countries I know, but these do not make a shoulder a sidewalk, or a carriageway a sidewalk. People must walk on the street in opposite direction without a sidewalk or shoulder, the text explicitly states that a shoulder is not a sidewalk. If there is only a shoulder, mapping an explicit footway with highway=footway would seem an error. The tag for mapping a shoulder is shoulder=* https://wiki.openstreetmap.org/wiki/Key%3Ashoulder
and the specifics are usually implicit (maybe depending on the country, typically it is forbidden to walk on motorways and motorroad=yes, for other roads the general default is access=yes, it may be restricted for more situations based on countryspecific rules).