Elasticsearch version 8.19.2

The bucket_script pipeline aggregation didn’t validate that its parent aggregation was a multi-bucket aggregation. This caused a ClassCastException at runtime when the parent was not multi-bucket. #132320 adds a validation step so the aggregation fails early, preventing the runtime error. (issue: #132272)

Merging shrink TSDB or LogsDB indices in versions 8.19 or 9.1+ could fail when using addIndexes to combine Lucene segments directly. In these cases, fieldInfos could differ between shards and the merged segment, causing incorrect merge statistics. PR #132597 updates the process to use fieldInfos from each segment instead of the merged segment, ensuring accurate stats and preventing merge failures.

In 8.19, the tsdb_doc_values_optimized_merge optimization was unintentionally disabled because its feature flag was not removed as planned. This happened when the original change failed to merge due to CI issues. #128459 removes the leftover flag, enabling the optimization as intended.

Strings parsed with the optimized UTF-8 parsing path had incorrect length calculations for characters outside the basic multilingual plane (BMP). These characters require two UTF-16 code units, but the optimized path did not account for this, causing mismatches with the non-optimized path. #132593 fixes the calculation to ensure consistent and correct string lengths.