[HUDI-8551] Support no precombine field with EVENT_TIME_ORDERING merge mode

[yihua]

Change Logs

This PR fixes the issue when the precombine field is not set with the merge mode of EVENT_TIME_ORDERING. Note that after #12600, there is no default of the precombine field config and it is no longer required for COMMIT_TIME_ORDERING. For EVENT_TIME_ORDERING, if the precombine field is not set, the logic should fall back to use the default ordering value of (int) 0 which has the highest priority (i.e., commit time ordering).

Detailed fixes include:

• Handles no precombine field when getting the ordering value in HoodieSparkRecord and HoodieAvroIndexedRecord to avoid NPE;
• Checks both empty and null for precombine field name to avoid issues;
• Considers empty ordering field specified by the Hudi Streamer when creating HoodieRecords from the Streamer.

New tests are added in TestMORDataSource and TestHoodieDeltaStreamer to cover the failure cases without this PR.

Impact

Supports no precombine field with EVENT_TIME_ORDERING merge mode.

Risk level

low

Documentation Update

Release docs will be updated.

Contributor's checklist

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

[nsivabalan]

can we de-couple partial update support w/ Commit time ordering and sql writes separately

Once we do that, we are good to land. changes LGTM otherwise.

[hudi-bot]

CI report:

• c1f8f96 Azure: SUCCESS

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