Since it's internal (nodoc'ed), maybe we should have `enum_attribute?` return the mapping (or `nil`) instead. (We call it `enum_mapping_for` or something more appropriate.)

So we'll have something like:

```
DEFINED_ENUMS = HWIA.new # :nodoc: Use HWIA here so we don't have to convert `attr_name` to symbols later

def enum_mapping_for(attr_name) # :nodoc:
  DEFINED_ENUMS[attr_name]
end
```