Add experimental Java 17 option to Initializr

[shai-almog]

Motivation

• The hellocodenameone example and related Maven build files were updated to Java 17, so the Initializr should offer a Java 17 project option while keeping the stable default unchanged.
• Java 17 support is not yet fully vetted, so the option must be clearly labeled experimental and disabled by default.

Description

• Added a ProjectOptions.JavaVersion enum with JAVA_8 and JAVA_17_EXPERIMENTAL, defaulting to JAVA_8, and carried the selection through ProjectOptions. (ProjectOptions.java)
• Exposed a new “Java Version” panel in the Initializr UI and wired the selection into generation and the settings summary; the default remains Java 8. (Initializr.java)
• Updated generation logic in GeneratorModel to apply Java-17-specific changes when JAVA_17_EXPERIMENTAL is selected: it sets codename1.arg.java.version=17 in common/codenameone_settings.properties and rewrites common/pom.xml compiler <source>/<target> from 1.8 to 17. (GeneratorModel.java)
• Extended GeneratorModelMatrixTest to add a validateExperimentalJava17Generation check and updated helper assertions to verify both default Java 8 outputs and the experimental Java 17 outputs. (GeneratorModelMatrixTest.java)

Testing

• Ran the Initializr module tests via Maven: cd scripts/initializr && mvn -pl common test -DskipTests=false, which failed due to a missing reactor artifact when building the module in isolation (initializr-ZipSupport not found). (failure)
• Tried the multi-module build: cd scripts/initializr && mvn -pl common -am test -DskipTests=false, which progressed but failed in this environment during the install-codenameone step with java.net.SocketException: Network is unreachable while attempting to download UpdateCodenameOne.jar; test execution could not complete here. (blocked by network/environment)
• Unit test coverage was updated: GeneratorModelMatrixTest now validates the experimental Java 17 generation behavior, but CI/local run is required to confirm green test results due to the environment limitations above.

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Codex Task

[github-actions]

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