Inline some type aliases in public API, part 2

[Allex-Nik]

Follow up of #906

The same as in #906 needs to be done, but for the following aliases as well:

• AnyCol,
• AnyColumnReference,
• AnyColumnGroupAccessor,
• StringCol,
• ColumnGroupReference

The changes should not include internal usages, and the declarations of the aliases themselves should not be removed. The main idea is to make code completion in the public API cleaner.

[yunhwane]

Hi! First-time contributor here — I'd like to take this, following the same approach as #906. Could you assign it to me? 🙌