GH-34315: [C++] Correct is_null kernel for Union and RunEndEncoded logical nulls#35036

jorisvandenbossche wants to merge 17 commits intoapache:mainapache/arrow:mainfrom

jorisvandenbossche:gh-34315-union-us_nulljorisvandenbossche/arrow:gh-34315-union-us_nullCopy head branch name to clipboard