support Dictionary types in approx_distinct #24730

Is your feature request related to a problem or challenge?

approx_distinct returns a not implemented error when the input column has a Dictionary type (e.g. Dictionary(Int32, Utf8)), which is common for low-cardinality string columns stored in Parquet or produced by joins/filters.
Today
SELECT approx_distinct(dict_col) FROM t;
Error: Support for 'approx_distinct' for data type Dictionary(Int32, Utf8) is not implemented

Describe the solution you'd like

approx_distinct uses create_hashes internally (via HLLAccumulator and HllGroupsAccumulator), which already handles Dictionary arrays correctly by hashing the logical decoded values. The fix is to route Dictionary(_, _) to HLLAccumulator

Describe alternatives you've considered

No response

Additional context

No response