[INLONG-7589][Sort] Support multi node relation with same output but different input nodes

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Prepare a Pull Request

• Fixes [Feature][Sort] Support multi node relation with same output but different input nodes  #7589

Motivation

Now it's not capable for sort to generate multi insert sqls for one output with multiple inputs which is not acceptable for user cases.

For instance, user may want to get data from multiple data sources, they can only use union operation for now. But union operation in flink is too heavy.

We need to support generate sqls from one stream such that:

Insert into sink select * from sourceA;
Insert into sink select * from sourceB;

Modifications

Change the parseNode to ParseSingleNode because the recuisive method will be multi branches which is not suitable for reading. And move the input nodes parsing outside of parseNode method to make it easy for reading

Verifying this change

Run AllmigrateTestMultiRelations