Update Union Array to add `UnionMode`, match latest Arrow Spec, and rename `new` -> `unsafe new_unchecked()`#885

Merged

alamb merged 4 commits intoapache:masterfrom alamb:alamb/union_fix

Jan 2, 2022

+247-81

Commits on Dec 20, 2021

Update union array to new null handling
alamb
committed

Commits on Jan 2, 2022