[FLINK-39782][table] Add SNAPSHOT built-in function definition and type inference

[fhueske]

What is the purpose of the change

Add SNAPSHOT built-in function definition and type inference for FLIP-579.

Brief change log

• Add SNAPSHOT function definition.
  • Function is added without a runtime implementation.
  • We will later add planner rules to rewrite it to the LateralSnapshotJoinOperator..
• Provide input and output type strategies for function
• Add tests for SNAPSHOT type strategies
• Add plan and execution tests using the SNAPSHOT function
  • Execution tests are failing as expected because we don't provide an implemenation for the function.

Verifying this change

Added unit tests.

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, adds a new built-in SQL function
• 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? no, documentation will be added when the feature works end-to-end

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Co-authored-by: Claude Code 2.1.148 (Opus 4.7)

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CI report:

• 1ec554a Azure: SUCCESS

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