Add support for looking up Classes and Methods on classpath

Currently vscode-java allows completion and introspection of Classes and Methods on-the-fly while editing your code. Afaik, currently the only way for someone to find the source of a class or method is to have the Class imported.

It would be amazingly helpful if you could find Classes, Interfaces (and their implementations) and methods that are available to you (i.e. configured on the classpath, either explicitly or via Maven dependencies).

Environment
  • Operating System: Windows 10
  • JDK version: Oracle JDK 8 Release 121
  • Visual Studio Code version: 1.12.1
  • Java extension version: 0.3.0
Steps To Reproduce

N/A, Feature request.