Add resolving of fileWorkspaceFolderBasename variable

[ahlinc]

This PR add the fileWorkspaceFolderBasename variable that would be useful in launch.json and task.json configurations. Especially it will be useful to create dynamic launch configurations when a binary name equals to a project root folder name.

Closes #159795

[ahlinc]

@microsoft-github-policy-service agree

[ahlinc]

It can be verified with:

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "echo",
            "type": "shell",
            "command": "echo",
            "args": ["${fileWorkspaceFolderBasename}"],
            "problemMatcher": []
        }
    ]
}

[meganrogge]

Works well, thanks