Diagnostics do not work on symlinked files

Syntax highlighting does not work on symlinked files, but it does on original one.

Environment

• Operating System: Ubuntu 20.04
• JDK version: 13.0.7
• Visual Studio Code version: 1.63.2
• Java extension version: 1.3.0

Steps To Reproduce

1. Create a sample java project with a .java file and introduce an error to it (e.g. use HashMap<String, String> without importing HashMap).
2. You should see HashMap underlined with an error HashMap cannot be resolved to a type
3. Create a symlink of the file to somewhere outside the project (in ubuntu: ln -s <path to original file> <path somewhere outside src/main/java structure>)
4. The new file won't have HashMap underlined

使用列出的 Ubuntu、JDK 和 VS Code 配置复现该问题，比较原始 .java 文件和符号链接 .java 文件上的诊断结果。跟踪 src/main/java 结构之外的文件是如何处理的；当符号链接文件显示与原始文件相同的诊断结果时，即视为完成。