Validate FUNCTIONS_WORKER_RUNTIME is defined

[asavaritayal]

After this message -

Prompt the user to pick a language for their project and initialize it as the FUNCTIONS_WORKER_RUNTIME setting in the local.settings.json file.

This'll ensure that the user is set up for success to run/debug functions locally.

[ejizba]

@asavaritayal I don't think the timing of that prompt matches up with what you want. That prompt happens because they have a project they created with the func cli (or elsewhere) and are opening it in VS Code for the first time. In many cases, FUNCTIONS_WORKER_RUNTIME should already be set.

I believe you want us to somehow validate for the case when local.settings.json is deleted because it's not tracked by source control (similar to Azure/azure-functions-core-tools#1261), but I'm not sure when that should happen. Also I think adding FUNCTIONS_WORKER_RUNTIME to source control is the true fix: Azure/azure-functions-host#3120

[ejizba]

Note to self: Did I fix this already?

[ejizba]

Fixed in #1431