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

Bắt đầu với issue #193 và truy vết cảnh báo hiện có "Classpath is incomplete" trong Java extension. Tái hiện cảnh báo này với nhiều thư mục dự án Java trong cùng một cửa sổ VS Code sau khi xóa tệp .project và làm sạch môi trường language server. Hoàn tất khi cảnh báo xác định được tệp hoặc thư mục liên quan.