Feature request: Support development of the OpenJDK class library

[simonis]

The OpenJDK class library has no Maven or Gradle build files. It is also a tricky project because its classes can interfere with the same classes in the JDK used to run javac in the language server.

Please add support for developing the Java class library of the OpenJDK project to your plugin.

[lahodaj]

This may work:

• open the module that you want to develop (e.g. src/java.base)
• add the corresponding test folder to the workspace (e.g. test/jdk)
• when running test, use "Run/Debug test" over the @test tag, not the possible Run/Debug main

There are probably some limitations and bugs in this, but this is the overall idea on how things should work. I could open java.lang.String like this, and use code completion in it, and debug a test for j.l.String. It would be awesome to hear some experiences.

(Opening the OpenJDK checkout as such might also work, but will lead to indexing for a high number of files, and generally might lead to worse performance.)