Optimize CASE expression to produce dictionary-encoded arrays in some cases

[andygrove]

Is your feature request related to a problem or challenge?

Here is an example CASE expression that produces an array containing exactly two distinct values:

CASE WHEN expr THEN 1 ELSE 0 END

We currently produce an array containing ones and zeros (and nulls). It seems like it would be beneficial to produce a dictionary-encoded array in this case to reduce memory pressure. This could also make subsequent operations more efficient in some cases.

[alamb]

I think implementing operations like this will be much easier if we are able to add LogicalTypes

#11513

(I am thinking specifically that we could have expressions dynamically decide what encoding to use for their output rather than having it hard coded)