[FLINK-39195][Table SQL/API] ObjectPath should implement Comparable

[Myracle]

What is the purpose of the change

This pull request makes ObjectPath implement the Comparable<ObjectPath> interface, enabling natural ordering of ObjectPath instances. This allows users to sort catalog object paths (e.g., in TreeMap, TreeSet, or Collections.sort()) by database name first, then by object name, which is useful when displaying or processing catalog objects in a deterministic order.

Brief change log

• Made ObjectPath implement Comparable<ObjectPath>, with comparison based on databaseName first and then objectName
• Added ObjectPathTest with comprehensive test cases covering comparison, sorting, transitivity, and consistency with equals

Verifying this change

This change added tests and can be verified as follows:

• Added ObjectPathTest with 8 test cases covering:
  • Comparison with different database names
  • Comparison with same database but different object names
  • Comparison with equal paths
  • Comparison with self
  • Consistency between compareTo and equals
  • Sorting behavior with Collections.sort()
  • Transitivity of the comparison
  • Database name takes precedence over object name in ordering

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 (ObjectPath is annotated with @PublicEvolving)
• 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? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• 1312f6e Azure: SUCCESS

Bot commands

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• @flinkbot run azure re-run the last Azure build

[rionmonster]

We may want to consider adding a series of Python tests for these operations to the existing CatalogTestBase if anything just to exercise these happy paths and any potential edge cases (e.g. comparisons against non-ObjectPath objects such as someObjectPath < 42 as I believe that might return False unexpectedly from the isInstance() check).