More control over completions (e.g., disable Java standard library method completions)

I would like to request a feature to allow fine-grained control over completions in the extension. Specifically, I want to disable completions for Java standard library methods (e.g., String.split(), System.out.println(), etc.) while keeping completions for my project's dependencies, such as Gradle plugins and custom libraries.

Currently, the java.completion.enabled setting disables all completions, which is not ideal for my workflow. I rely heavily on Gradle plugin completions, and the Java standard library methods cannot be used in my project.

issue 中没有指定文件或测试。首先定位 java.completion.enabled 设置和扩展的补全处理逻辑，然后确定如何区分 Java 标准库方法与项目依赖项的补全；完成的标准是抑制标准库示例，同时保留 Gradle 插件和自定义库的补全。