support relative paths when configuring jdk

my project's jdk is located in a directory relative to the project root, but specifying a relative path does not seem to be supported:

{
    "java.jdt.ls.java.home": "./jdk"
    // also doesn't work:
    // "java.jdt.ls.java.home": "${workspaceFolder}/jdk"
}

it would be nice if i could do this because it would allow me to commit this in my workspace settings.json so that others working on my project don't have to configure the path to their jdk manually, since it's located in the same spot for everybody

首先定位扩展对 java.jdt.ls.java.home 设置的处理方式，以及 workspace 路径的解析方式。在 workspace 的 settings.json 中检查 ./jdk 和 ${workspaceFolder}/jdk 两者的行为，然后验证相对于项目的 JDK 路径对其他贡献者也能一致地工作。