HIVE-29560: Fix JdbcColumn DECIMAL class mapping to BigDecimal

[kezhuoquan]

What changes were proposed in this pull request?

JdbcColumn.columnClassName() currently maps Types.DECIMAL to
BigInteger.class.getName(), which is incorrect for DECIMAL semantics.
This PR changes the mapping to BigDecimal.class.getName().

Why are the changes needed?

JDBC DECIMAL should map to java.math.BigDecimal, not BigInteger.
The current behavior may cause type mismatch and incorrect metadata
interpretation by JDBC clients.

Does this PR introduce any user-facing change?

Yes.
For DECIMAL columns, JDBC metadata now reports
java.math.BigDecimal as the column class name.

How was this patch tested?

• Built JDBC module successfully:
  • mvn -pl jdbc -DskipTests compile
• Verified code change in:
  • jdbc/src/java/org/apache/hive/jdbc/JdbcColumn.java

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
Feel free to reach out on the dev@hive.apache.org list if the patch is in need of reviews.