approx_distinct should be leveraging bitmap for counting u8/16 and i8/16

[jimexist]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
(This section helps Arrow developers understand the context and why for this feature, in addition to the what)

approx_distinct should be leveraging bitmap for counting u8/16 and i8/16

Describe the solution you'd like

Using a bitmap is more efficient

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[alamb]

See code at https://github.com/apache/arrow-datafusion/blob/397110ab6948ea80a14155d65acaf55e23fd624e/datafusion/src/physical_plan/expressions/approx_distinct.rs#L88-L91

[Weijun-H]

Why don't we also support u32/i32 🤔 ?

[alamb]

there is no reason I know of