Editing classpath file requires restart of VS Code

Originally created by @VanessaLange at Microsoft/vscode-java-debug#576

When adding a jar to the classpath file the program won't build any longer and you get the error message: "Build failed, do you want to continue?" You have to restart VS Code before it works again.

Environment

• Operating System: macOS Mojave Version 10.14.4 (also Windows 10)
• JDK version: openjdk version "1.8.0_212"
• Visual Studio Code version: 1.33.1
• Java extension version: 0.43.0
• Java Debugger extension version: 0.17.0

Steps To Reproduce

1. Create a new Java Project
2. Add a jar to the classpath
3. Try to run the program

Current Result

The build fails and you cannot run the program.

Expected Result

Either building works out of the box when editing the classpath or at least we get a message that restarting VS Code is required.

Additional Informations

The language server is loaded correctly (thumbs up icon).

Reproduce the failure in a new Java Project by adding a jar to the classpath and running the program in VS Code. Trace how the Java extension handles classpath edits and build state; done means the project builds and runs without restarting VS Code, or clearly reports when a restart is required.