coreclr debug configuration should support input variables for `envFile`

VS Code has a mechanism called “input variables” where debug configuration values can be resolved by running arbitrary commands, picking an item from predefined list, or prompting the user: https://code.visualstudio.com/docs/editor/variables-reference#_input-variables

Node.js and Python debug configuration providers support this mechanism. Unfortunately, coreclr seems to lack this support.

Repro steps

1. Create a debug configuration that uses an input variable, for example

{
    "configurations": [
        {
            "name": "Debug API",
            "type": "coreclr",
            "request": "launch",
            // other properties as necessary
            "envFile": "${input:getPathToFile}"
        }
    ],
    "inputs": [
        {
            "id": "getPathToFile",
            "type": "promptString"
             // The really interesting/important case is type==command.
             // promptString is used just to simplify the repro
         }
    ]
}

1. Try using the configuration

Expected result

Should prompt the user for the path to the .env file

Actual result

Can't parse envFile ${input:getPathToFile} because of Error: ENOENT: no such file or directory, open '${input:getPathToFile}'

[gregg-miskelly]

@karolz-ms Sounds great

[connor4312]

js-debug handles it at launch time, but you could also change this extension to resolve envFile after variables are substituted via the relatively-new post-substitution method in the resolver.