[FLINK-39196][pipeline-connector][oracle] Support change column nullable without data type

[zml1206]

Oracle support change column nullable without data type, for example

ALTER TABLE t MODIFY a NULL

[zml1206]

@lvyanquan Can you help take a look? I'm not sure if getting a table column dataType from historyRecord is reliable.

[Copilot]

Pull request overview

This PR adds Oracle support for ALTER TABLE ... MODIFY <col> NULL/NOT NULL statements that omit the column data type (e.g., ALTER TABLE t MODIFY a NULL) by ensuring the parser can reuse the existing column schema.

Changes:

• Extend Oracle connector IT coverage to include changing a column from NOT NULL to NULL without specifying a data type.
• Update the Oracle ALTER TABLE parser to look up the existing column definition and only require a datatype when the column schema is missing.
• Hydrate/refresh the in-memory Tables cache in the Oracle event deserializer using Debezium HistoryRecord TABLE_CHANGES, enabling parsing of datatype-omitted ALTERs.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
.../OraclePipelineITCase.java	Adds an integration test sequence that exercises MODIFY <col> NULL without datatype and updates expected schema-change events accordingly.
.../OracleAlterTableParserListener.java	Switches to editing/creating tables from Debezium’s databaseTables() and enables MODIFY ... NULL parsing by editing existing column schema when available.
.../OracleEventDeserializer.java	Preloads Tables state from HistoryRecord.Fields.TABLE_CHANGES so the parser has column schemas available during ALTER parsing.

Comments suppressed due to low confidence (1)

flink-cdc-connect/flink-cdc-pipeline-connectors/flink-cdc-pipeline-connector-oracle/src/test/java/org/apache/flink/cdc/connectors/oracle/source/OraclePipelineITCase.java:1740

• The schema name argument is inconsistent here ("DEBEZIUM" vs "debezium" used throughout the rest of this test). Even though Oracle treats unquoted identifiers case-insensitively, keeping the casing consistent avoids confusion and makes the intent clearer.

        statement.execute(String.format("ALTER TABLE %s.products MODIFY DESC1 NULL", "DEBEZIUM"));

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[lvyanquan]

CC @linjianchang as you may be interested in this.