[C++] Add a Dictionary Compaction Function For DictionaryArray

[R-JunmingChen]

Describe the enhancement requested

DictionaryArray could have unused dictionary values. This is an obstacle to finish #37100. A Dictionary Compaction Function, which removes unused values in dictionary, is useful to solve the problem. Besides, apache/arrow-go#49 has the same request in Go implementation.

Here is a pesudo example:

dict_a
dictionary: ["1", "2", "3"]
indices: [0, 1, 0, 1]

dictionary_compaction(dict_a)
dictionary: ["1", "2"]
indices: [0, 1, 0, 1]

Component(s)

C++