#AI commit# CC: 修复getProps方法先调用mappings()再序列化 / Fix getProps to call mappings() before serialization

## 问题 / Problem
getProps方法中直接对IndexMappingRecord序列化，没有先调用mappings()获取TypeMapping

## 修复 / Fix
- 先调用mappingRecord.mappings()获取TypeMapping对象
- 然后对TypeMapping进行JsonpUtils.toJsonString序列化

## 原因 / Reason
IndexMappingRecord包含索引级别的元数据，而mappings()返回的TypeMapping才是实际的字段映射定义。
直接序列化IndexMappingRecord会包含多余的结构，导致后续获取properties时路径不正确。

Fix getProps method to call mappings() on IndexMappingRecord before JsonpUtils.toJsonString serialization.
The mappings() method returns TypeMapping which contains the actual field mapping definitions,
while IndexMappingRecord includes additional index-level metadata.

Author: Davidhua1996

exchangis-engines/engines/datax/datax-elasticsearch8xwriter/src/main/java/com/webank/wedatasphere/exchangis/datax/plugin/writer/elasticsearchwriter/v8x/Elastic8xRestClient.java

@@ -365,7 +365,9 @@ public Map<Object, Object> getProps(String indexName, String typeName) {
             GetMappingResponse response = esClient.indices().getMapping(request);
             IndexMappingRecord mappingRecord = response.get(indexName);
             if (null != mappingRecord){
-                String mappingJson = JsonpUtils.toJsonString(mappingRecord, esClient._jsonpMapper());
+                // 先调用mappings()获取TypeMapping，再序列化为JSON
+                // First call mappings() to get TypeMapping, then serialize to JSON
+                String mappingJson = JsonpUtils.toJsonString(mappingRecord.mappings(), esClient._jsonpMapper());
                 Map<String, Object> mappingMap = Json.fromJson(mappingJson, Map.class);
                 if (null != mappingMap){
                     Object props = mappingMap.get(FIELD_PROPS);