[FLINK-37914][table] Add built-in OBJECT_UPDATE function

[raminqaf]

What is the purpose of the change

This pull request implements the OBJECT_UPDATE built-in function as part of FLIP-520: Simplify StructuredType handling. The function allows users to update existing fields in structured objects by providing key-value pairs, enabling mutation operations on structured types in both SQL and Table API without requiring custom UDFs.

Brief change log

• Added ObjectUpdateInputTypeStrategy for validating input arguments (structured object + key-value pairs)
• Added ObjectUpdateTypeStrategy for inferring return types (same as input structured type)
• Implemented ObjectUpdateFunction runtime function for performing field updates
• Added OBJECT_UPDATE to BuiltInFunctionDefinitions with proper type inference strategies
• Added Table API expression support via objectUpdate() method on expressions
• Updated SQL and Table API documentation with examples and usage patterns
• Added comprehensive validation for field names, types, and compatibility checking
• Implemented proper error handling for non-existent fields and type mismatches

Verifying this change

This change added tests and can be verified as follows:

• Added unit tests in ObjectUpdateInputTypeStrategyTest for input validation scenarios
• Added integration tests in StructuredFunctionsITCase for end-to-end SQL functionality

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 (new built-in function)
• The serializers: no
• The runtime per-record code paths (performance sensitive): yes (new scalar function execution)
• 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 / JavaDocs (updated SQL functions documentation and comprehensive JavaDoc comments)

[flinkbot]

CI report:

• d8894e4 Azure: SUCCESS

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[twalthr]

Last review comment. Almost there :-)

[twalthr]

Thanks for the update @raminqaf. LGTM.