Unify the names of methods that receive/return strings

[sashacmc]

Describe the release item

• str for char */ const char * (e.g. z_bytes_serialize_from_str)
• string for z_owned_string_t/z_loaned_string_t (e.g. z_bytes_deserialize_into_string)
• view_string for z_view_string_t (e.g. z_whatami_to_view_string)