[FEA] Dictionary type support for row_bit_count

[jihoonson]

Is your feature request related to a problem? Please describe.
row_bit_count currently does not support the dictionary type.

Describe the solution you'd like
It seems that we could add a new flatten_functor specialized for the dictionary type in here.

Describe alternatives you've considered
I have not considered alternatives.

Additional context
When row_bit_count fails because of unsupported data types, it does not say what is the type unsupported. It would be nice to include the name of the unsupported type in the error message.