Fix character encoding problem for non-ASCII/Chinese data (#795)

[sanjaykumarmtt]

### Motivation
Fixes #795

When reading Chinese or other multi byte characters from DB2 they show up as ??? because the driver only checked OS type instead of the server CCSID.

This change fixes the issue:

• Maps DB2 CCSID numbers to Java Charset in CCSIDConstants.
• Uses server column CCSID (sda.ccsid_) if present; otherwise, uses connection level encoding (getCcsidMbcEncoding()).

Conformance

• I have signed the Eclipse Contributor Agreement (ECA).
• Followed code style and tested with DB2 database.

[tsegismont]

Thank you @sanjaykumarmtt

Could you please add a test?

[sanjaykumarmtt]

​@tsegismont thank you for the review I have added the unit test and formatted the code accordingly

[tsegismont]

Thanks for adding a test, but I was thinking about actually testing a DB2 query rather than a unit test. Is it possible?

[sanjaykumarmtt]

thanks for the feedback @tsegismont yes that makes sense I will add a DB2 query integration test for this and update the PR soon

[sanjaykumarmtt]

hi @tsegismont ​apologies for the delay I have replaced the previous unit test with a DB2 query integration test in DB2QueriesTest as suggested please review it and let me know if any further changes are needed

[sanjaykumarmtt]

​I have updated the PR with the suggested fix: casting the untyped parameter marker with CAST(? AS VARCHAR(100)) in DB2QueriesTest, and reverted the unrelated changes.
​Could you please approve and trigger the CI workflow when you have a moment?

[tsegismont]

Thanks. For me the test passes without the code changes. Can you check if it's actually testing what you want?