Support ${WorkspaceFolder:<folder>} in settings

[dseynhae]

I have a workspace where I have multiple folders... Some of those folders are where my libraries are stored.

{
"folders": [
    {
      "path": "/a/b/c/d/e/f/lib1",
    },
    {
      "path": "/q/r/s/t/lib2",
    },
   ],
}

However, in the settings, the syntax is not understood:

{
"settings": [
    {
      "perl.perlInc": [
         "${workspaceFolder:lib1}",
      ]
    },
   ],
}

I need to spell it out:

{
"settings": [
    {
      "perl.perlInc": [
         "/a/b/c/d/e/f/lib1",
      ]
    },
   ],
}

Even if I spell out the name for the workspace folder, it doesn't help:

{
"folders": [
    {
      "name": "lib1",
      "path": "/a/b/c/d/e/f/lib1",
    },
    {
       "name": "lib2",
      "path": "/q/r/s/t/lib2",
    },
   ],
}

[grahamc]

re https://github.com/microsoft/vscode/issues/2809