[FLINK-12073][table-planner-blink] Support appropriate precision and scale processing of Decimal

[JingsongLi]

What is the purpose of the change

1.Make Decimal's output more precise than random.
2.Let Decimal process closer to mainstream databases such as Hive/SqlServer.

Verifying this change

ut

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, Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (yes)
• If yes, how is the feature documented? (JavaDocs)

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[KurtYoung]

Why not calling it DecimalTypeInfo ?

[JingsongLi]

I think it is a TypeInfo for BigDecimal, so BigDecimalTypeInfo is more appropriate.

[godfreyhe]

LGTM