The delegate accepts the collection or DataTable to select columns.
The delegate returns different types of values to describe selected columns:

• Returns IEnumerable<T> of DataColumn to select columns for the specified DataTable.
• Returns IEnumerable<T> of int to select columns by indexes for the specified DataTable.
• Returns IEnumerable<T> of string to select columns by names for the specified DataTable, dictionary or custom object. This option is not AOT-compatible for custom objects.
• Returns IEnumerable<T> of property getter Delegate (where the delegate type of each element is Func<T, TResult>, T is the element type of collection, TResult is the property type) to select columns with custom column getters.
  In this case, IncludeColumnsHeader must be false. Otherwise, an exception will be thrown. Because we don't know the column names.
• Returns IEnumerable<T> of named property getter (T1, T2) (where T1 is column name string, T2 is property getter Delegate; The delegate type of each element is Func<T, TResult>, T is the element type of collection, TResult is the property type) to select columns with custom column names and custom column getters.
  In this case, IncludeColumnsHeader should be true. Otherwise, the column names will be ignored.