### Describe the enhancement requested Some [CTypeTraits](https://github.com/apache/arrow/blob/7ba1a7b99b3c036d9d14d345876cfe7194ecaacc/cpp/src/arrow/type_traits.h#L101-L102) are missing in `type_traits.h`, e.g. all decimal types. May need to add them. ### Component(s) C++