Allow to define directory mapping for remote debugging

[Nowaker]

• File path in my development environment: /home/nowaker/projekty/dreamhost/ndn/bin/ndn-dev
• File path in the Docker container: /home/ndn/bin/ndn-dev

This is what happens when I hit the first breakpoint:

Config:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "perl",
      "request": "launch",
      "name": "Perl-Debug",
      "console": "remote",
      "port": 9000,
      "root": "${workspaceFolder}",
      "program": "${workspaceFolder}/${relativeFile}",
      "stopOnEntry": true,
      "reloadModules": false
    }
  ]
}

We need a way to define directory mappings, for example:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "perl",
      "request": "launch",
      "name": "Perl-Debug",
      "console": "remote",
      "port": 9000,
      "root": "${workspaceFolder}",
      "dirMapping": [
        {"/home/ndn": "${workspaceFolder}"},
        {"/some/remote/path": "/some/local/path"}
      ],
      "program": "${workspaceFolder}/${relativeFile}",
      "stopOnEntry": true,
      "reloadModules": false
    }
  ]
}