[INLONG-8436][Sort] Fix the backfill task not running bug in oracle cdc connector

[e-mhui]

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[INLONG-8436][Sort] Fix the backfill task not running bug in oracle cdc connector

• Fixes [Bug] The backfill task not running bug in oracle cdc connector #8436

Motivation

Fix the backfill task not running bug in oracle cdc connector.

Modifications

1. In the OracleScanFetchTask#doExecute method, for Snapshot step 3, we need to set the highWatermark instead of the lowWatermark.

((SnapshotSplitChangeEventSourceContext) (context)).setHighWatermark(highWatermark);

2. The RedoLogSplitReadTask should use the StartingOffset of RedoLogSplit instead of the StartingOffset of SnapshotSplit.

            final RedoLogSplitReadTask backfillRedoLogReadReTask =
                    createBackfillRedoLogReadTask(backfillRedoLogSplit, sourceFetchContext);
            final LogMinerOracleOffsetContextLoader loader =
                    new LogMinerOracleOffsetContextLoader(
                            ((OracleSourceFetchTaskContext) context).getDbzConnectorConfig());
            final OracleOffsetContext oracleOffsetContext =
                    loader.load(backfillRedoLogSplit.getStartingOffset().getOffset());
            backfillRedoLogReadReTask.execute(
                    new SnapshotStreamSplitChangeEventSourceContext(), oracleOffsetContext);