Suport environment variables in `jdk.project.jdkhome` settings

[balthild]

I use nix to manage dev environments, so there's no simple and predictable java home paths. The paths are subject to change each time I update the packages. Therefore, I wish to have a way setting the jdk path from a specific environment veriable.

There's a standard syntax in vscode to do this, i.e.

{
  "jdk.project.jdkhome": "${env:JAVA_HOME_PROJECT}"`
}

However, It is not substituted in config.json out of the box. Therefore, extensions need to do it by themselves, e.g. https://github.com/DominicVonk/vscode-variables.

[Achal1607]

Hey @balthild,
Thanks for using our extension. As mentioned in the README, we currently read a few environment variables to set the JDK home. As a workaround, you can use these for now, but we plan to extend support for VSCode's environment variable syntax in the future.

[balthild]

This doesn't work when the language server and the project need to use different JDKs.