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

Riprodurre il problema aprendo sorgenti sotto jdk/src/share/classes, ad esempio java/lang/String.java, con JDK 8 e 11 nelle versioni indicate di VS Code e dell’estensione Java. Esaminare come l’estensione gestisce le sorgenti della libreria standard e le diagnostiche di moduli e package; il lavoro è completato quando quei file possono essere modificati e percorsi senza gli errori segnalati.