Configured debug type 'extensionHost' is not supported.

[thealjey]

I'm trying to follow the Your First Extension guide for the first time.
And the very first thing they tell you to do (Inside the editor, open src/extension.ts and press F5) results in the following:

Obviously, the Install extensionHost Extension button doesn't help at all, because there's no such extension in the Marketplace.
...
Why does nothing ever work on the first try? 😭