[FLINK-27015][hive] Fix exception for casting timestamp to decimal in Hive dialect

[luoyuxia]

What is the purpose of the change

Support insert timestamp type to decimal type in Hive dialect.

Brief change log

• Add a custome udf flink_hive_to_decimal to convert other datatypes include timestamp to decimal
• When it's for insert timestamp to decimal, make it to be a RexCall to call function flink_hive_to_decimal

Verifying this change

Added test in ...connector-hive/src/test/java/org/apache/flink/connectors/hive/HiveDialectQueryITCase.java#testInsertTimeStampToDecimal

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? no

//todo for : CAST(ctimestamp1 AS DECIMAL(15,0))

[flinkbot]

CI report:

• 96bb60ca6ec6be5931cb513780c131763538eea9 Azure: FAILURE

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