Add '$workspaceName' placeholder

[ghost]

This pull request adds $workspaceName placeholder that has to be replaced by the name of the folder opened in VS Code. If no folder is opened, it will be replaced with the directory name of the code file.

Example:

"code-runner.executorMap": {
    "haskell": "cd $workspaceRoot && stack build && stack exec $workspaceName-exe"
}

[Sbrjt]

I could do it using fileWorkspaceFolder:

        "typescriptreact": "cd \"${fileWorkspaceFolder}\" && npm run dev"