Fix ExprEval of BigDecimal data type

[maytasm]

Fix ExprEval of BigDecimal data type

Description

This PR fixes a regression caused by #13947 (more specifically at https://github.com/apache/druid/pull/13947/files#diff-199493eb5b59a386d1fcade78da6578074cd94c80c114cfdd875a218106ca302L127 was changed to https://github.com/apache/druid/pull/13947/files#diff-5be9af304a8dda2062ca806bcc5320628757609c441fee5aec6e1ce51f71ded6R120)
Previously, we were just returning the raw but now we are using the method bestEffortOf which incorrectly handle BigDecimal data type. BigDecimal data type is incorrectly converted to Long. This issue was discovered with ingestion of Parquet files which use BigDecimal data type

Key changed/added classes in this PR

processing/src/main/java/org/apache/druid/math/expr/ExprEval.java

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[gianm]

LGTM, seems like a reasonable thing to do for bestEffortOf, since there isn't a native big-decimal type.