Add support for resolving old or new record when ordering field matches with MERGE MODEs

### Describe the problem you faced

We are adding support to payloads, where users can configure which record to resolve (old or new) when ordering field matches https://github.com/apache/hudi/pull/18413

we might need a similar fix for MERGE MODEs as well

### To Reproduce

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### Expected behavior

Based on the configuration set, the right record should be chosen.

### Environment Description

* Hudi version:
* Spark version:
* Flink version:
* Hive version:
* Hadoop version:
* Storage (HDFS/S3/GCS..):
* Running on Docker? (yes/no):

### Additional context

_No response_

### Stacktrace

```shell

```

Review the referenced PR #18413 and locate the Hudi merge-mode handling for ordering-field matches; this issue names no source file or test. Clarify the expected old/new record selection for each configuration, then add focused coverage showing that MERGE MODE chooses the configured record.

Written by the indexing model from the issue text.