Add Java Platform Module System (JPMS) Support

从 function-maven-plugin/src/main/java/com/google/cloud/functions/plugin/RunFunction.java 中硬编码的 classpath 配置开始。跟踪 Invoker CLI 和 Maven/Gradle 插件如何启动函数，然后确定 module-path 配置必须如何传递到云运行时。完成这项工作需要协调支持本地调用、构建工具和云端执行。

Add support for running functions on the module path (--module-path) instead of only the classpath (--classpath) to enable full Java Platform Module System (JPMS) features in the Functions Framework.

Currently, the Functions Framework for Java only supports classpath-based execution, which prevents developers from utilizing JPMS features at runtime even when their code is properly modularized with module-info.java files.

Modern Java applications using JPMS face the following issues:

1. module-info.java files are ignored at runtime (treated as regular classes on classpath)
2. provides...with service provider declarations don't work, requiring fallback to legacy META-INF/services files
3. Module encapsulation and strong accessibility rules are not enforced
4. No module-level dependency management or version conflict resolution
5. Cannot leverage jlink to create optimized custom runtime images with only required modules, resulting in larger deployment artifacts

This feature request requires changes across three layers:

1. Local Development (Invoker CLI) - Add --module-path support
2. Build Tooling (Maven/Gradle plugins) - Add module-path configuration (right now classpath is hardcoded here
3. Cloud Runtime Infrastructure - Update Google Cloud Functions runtime to support modular execution