Note: migrated from original JIRA: https://issues.apache.org/jira/browse/ARROW-9324

The implementation of Union in arrow has evolved from the current arrow-rs implementation. We need to update arrow-rs to follow the updated Arrow spec, including the updated validity bitmap changes from https://issues.apache.org/jira/browse/ARROW-9222

Related: Null/Sparse Union Array support: #814

As part of implementing the new Union handling, we should also update the checks in ArrayData::validate added in #810