c256cca6f1
`expression` is a std::variant with 16 different variants that represent different types of AST nodes. Let's add documentation that explains what each of these 16 types represents. For people who are not familiar with expression code it might not be clear what each of them does, so let's add clear descriptions for all of them. Signed-off-by: Jan Ciolek <jan.ciolek@scylladb.com> Closes scylladb/scylladb#15767