[HUDI-4897] Refactor the merge handle in CDC mode

[danny0405]

Change Logs

Describe context and summary for this change. Highlight if any code was copied.

Impact

Describe any public API or user-facing feature change or any performance impact.

Risk level: none | low | medium | high

Choose one. If medium or high, explain what verification was done to mitigate the risks.

Contributor's checklist

• [ ] Read through contributor's guide
• [ ] Change Logs and Impact were stated clearly
• [ ] Adequate tests were added if applicable
• [ ] CI passed

[xushiyan]

Follow up for https://github.com/apache/hudi/pull/6697

[hudi-bot]

CI report:

• ebb7fa695913266b919f7d680a60bab5dc8d64d0 Azure: SUCCESS

Bot commands

@hudi-bot supports the following commands:

• @hudi-bot run azure re-run the last Azure build