[FLINK-11124][table] Add private[flink] to TemporalTableFunction.create() method

[hequn8128]

What is the purpose of the change

This pull request adds private[flink] to TemporalTableFunction.create() method. As TemporalTableFunction is an user-oriented class. I think it would be better to add private[flink] to the TemporalTableFunction.create() method in order to make it invisible to users.

Brief change log

• Add private[flink] to TemporalTableFunction.create()

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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? (no)

[twalthr]

Thank you @hequn8128. I will merge this. However, this only helps for Scala users not Java users. But this is a different topic.

[hequn8128]

@twalthr Thanks a lot for the review and merge.