Improvement: Classpath is Incomplete warning should give more context

Issue #193 points out that this message can be less than helpful. The wiki points out that this occurs when opening individual java files. But the cases associated with this message suggest there are various other conditions - missing .project files, misconfigured .classpath, among others. I have an environment where I open multiple project directories in a single vscode window. I don't even know which project to start looking at when this message appears.

It would be helpful if the message could display "Classpath is incomplete" in (File or directory reference)

Environment

• Operating System: OSX
• JDK version: jdk 1.8
• Visual Studio Code version: 1.35.1
• Java extension version: 0.46.0

Steps To Reproduce

1. With (say) 3 java project directories in a vscode window, delete .project in one.
2. Java: Clean the language server environment

"Classpath is Incomplete" warning is displayed

Current Result

Expected Result

Additional Informations

Beginne mit Issue #193 und verfolge die bestehende Warnung "Classpath is incomplete" in der Java extension. Reproduziere sie mit mehreren Java-Projektverzeichnissen in einem VS Code-Fenster, nachdem du eine .project-Datei gelöscht und die Umgebung des Language Servers bereinigt hast. Fertig ist es, wenn die Warnung die relevante Datei oder das relevante Verzeichnis identifiziert.