Improve flat_object field parsing performance by reducing two passes to a single pass (opensearch-project#16297)

Signed-off-by: panguixin <[email protected]>

Author: bugmakerrrrrr

CHANGELOG.md

@@ -26,6 +26,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Introduce framework for auxiliary transports and an experimental gRPC transport plugin ([#16534](https://github.com/opensearch-project/OpenSearch/pull/16534))
 - Support searching from doc_value using termQueryCaseInsensitive/termQuery in flat_object/keyword field([#16974](https://github.com/opensearch-project/OpenSearch/pull/16974/))
 - Added a new `time` field to replace the deprecated `getTime` field in `GetStats`. ([#17009](https://github.com/opensearch-project/OpenSearch/pull/17009))
+- Improve flat_object field parsing performance by reducing two passes to a single pass ([#16297](https://github.com/opensearch-project/OpenSearch/pull/16297))
 - Improve performance of the bitmap filtering([#16936](https://github.com/opensearch-project/OpenSearch/pull/16936/))
 - Added ability to retrieve value from DocValues in a flat_object filed([#16802](https://github.com/opensearch-project/OpenSearch/pull/16802))
 - Added new Setting property UnmodifiableOnRestore to prevent updating settings on restore snapshot ([#16957](https://github.com/opensearch-project/OpenSearch/pull/16957))