Can't edit/navigate standard Java class library files

This extension doesn't seem to support editing the Java class library files themselves (e.g. java/lang/String.java). When I open such a file, I get a lot of errors starting from the package/import declarations ("The package java.lang conflicts with a package accessible from another module: java.base") up to all the other standard classes which are referenced in the sources ("DeflaterOutputStream cannot be resolved to a typeJava(16777218)").

Is there a simple way to configure this extension in such a way that it allows editing/navigating the standard Java class library files?

Environment

• Operating System: Ubuntu 18.0.4
• JDK version: 8/11
• Visual Studio Code version: 1.39.2
• Java extension version: Java Extension Pack 0.8.0, Language Support for Java(TM) by Red Hat 0.52.0

Steps To Reproduce

1. open a directory with standard Java class library files (e.g. "jdk/src/share/classes" after cloning jdk from http://hg.openjdk.java.net/jdk8u/jdk8u/jdk

使用指定版本的 VS Code 和 Java 扩展，在 JDK 8 和 11 下打开 jdk/src/share/classes 下的源文件（例如 java/lang/String.java），以复现该问题。调查该扩展如何处理标准库源文件以及模块/包诊断；完成的标准是可以编辑这些文件并在其中导航，且不会出现所报告的错误。