Exposing project classpath information

[ChrisTrenkamp]

Original issue: redhat-developer/vscode-java#934

For other plugins (e.g. SonarLint) to support Java, the classpath information needs to be exposed.

Here's an example of what needs to be exposed. https://docs.sonarqube.org/display/PLUG/Java+Plugin+and+Bytecode.

[jdneo]

Has been supported at the Java Language Server side. See: redhat-developer/vscode-java#1212