[FLINK-26940][table] Add the built-in function SUBSTRING_INDEX

[dylanhz]

What is the purpose of the change

Add SUBSTRING_INDEX supported in SQL & Table API.
Examples:

> SELECT substring_index('www.apache.org', '.', 2);
 www.apache 

Brief change log

FLINK-26940

Verifying this change

This change added tests and can be verified as follows: StringFunctionsITCase#substringIndexTestCases

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): yes
• 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? yes
• If yes, how is the feature documented? docs

[flinkbot]

CI report:

• 944b606 Azure: SUCCESS

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[superdiaodiao]

Maybe we should also support API for Python? If so, you could refer other functions in these two files:

• docs/reference/pyflink.table/expressions.rst
• pyflink/table/expression.py

[lsyldliu]

@dylanhz Thanks for your contribution, I left some comments.

[lsyldliu]

Do we should check the str.length > target.length?

[dylanhz]

I believe it is unnecessary, as the current code would return -1 directly in this case, indicating no matching substring found, which aligns with the expected behavior.

[dylanhz]

BTW, I do find a bug in the next row, beginIndex < endIndex should be beginIndex <= endIndex. Corresponding test cases have been added.

[lsyldliu]

Can use the BinaryStringData to judge and find the substring instead of materialized it in advance?

[dylanhz]

Currently we don't have find and rfind for BinaryStringData. I think it would be great to introduce them into BinaryStringDataUtil because they are commonly used for string matching.