[C++] Split Type::UNION into Type::SPARSE_UNION and Type::DENSE_UNION #25003
Description
Similar to the recent Type::INTERVAL split, having these two array types which have different memory layouts under the same Type::type value makes function dispatch somewhat more complicated. This issue is less critical from INTERVAL so this may not be urgent but seems like a good pre-1.0 change
Reporter: Wes McKinney / @wesm
Assignee: Ben Kietzman / @bkietz
PRs and other links:
Note: This issue was originally created as ARROW-8866. Please see the migration documentation for further details.