Cannot get children from user library node

[Vigilans]

Related issue #174

After adding user library(CHECKSTYLE) in Eclipse:

The dependency viewer can show the container node, but not the jar files within it:

[Vigilans]

Cause of this behavior:

• The preferences specified in Eclipse are stored in /{my-eclipse-workspace}/.metadata/.plugins/org.eclipse.core.runtime/.settings
• The preferences used by language server are stored in the temporary workspace folder in workspaceStorage, as follows:
  

So in fact, vscode-java cannot make use of another workspace's user library settings.

Maybe we should provide a way for a user to specify the user libraries used in workspace.