[GH-2509] Refactor the example projects to include better examples

[jiayuasu]

Did you read the Contributor Guide?

• Yes, I have read the Contributor Rules and Contributor Development Guide

Is this PR related to a ticket?

• Yes, and the PR name follows the format [GH-XXX] my subject. Closes Update the example projects to include more examples #2509

What changes were proposed in this PR?

This pull request updates the Flink and Java Spark SQL example projects by modernizing dependencies, improving test coverage, cleaning up code, and enhancing build and CI configurations. Key changes include upgrading Spark and Sedona, refactoring the Flink example and utilities, adding Flink unit tests, and tightening Maven and CI setups.

Dependency and Configuration Updates
• Upgraded Spark, Sedona, Scala, and JUnit in the Java Spark SQL example and added Java 17+ compatibility settings.
• Switched dependency artifacts to use variables for better compatibility.

Flink Refactoring
• Cleaned up FlinkExample.java and Utils.java for clearer structure and extracted core logic into a testable method.

Testing
• Added FlinkFunctionsTest.java to validate S2 spatial joins across dataset sizes.

Build and Formatting
• Set Flink dependencies to provided and added Spotless and Surefire plugins for formatting and test execution.

CI Workflow
• Updated the example workflow to use mvn test, removed unused Java options, improved job naming, and split testing for Java, Scala, and Flink examples.

How was this patch tested?

Did this PR include necessary documentation updates?

• No, this PR does not affect any public API so no need to change the documentation.