Fix issue with missing "workers" directory

Recently, we updated how we build the minified core tools projects ([here](https://github.com/Azure/azure-functions-core-tools/commit/b4e66eb3370e6217d76290ad38726e7a3a380857)). Previously, we would build with all workers and then empty the "workers" directory. The change linked above changed that to not add workers for minified runtimes, which seems the right way to do it.

However, this broke a couple of scenarios where if a user does not have `FUNCTIONS_WORKER_RUNTIME` set, the minified package would throw an error as the host isn't able to get the worker information from the "workers" directory. Just having an empty "workers" directory fixes this issue.

We made a quick fix to revert this here -- https://github.com/Azure/azure-functions-core-tools/pull/2378
But, we should come up with the proper approach to tackle this.

Inspect the minified runtime build change in commit b4e66eb3370e6217d76290ad38726e7a3a380857 and compare it with the workaround in pull request 2378. Reproduce the scenarios where FUNCTIONS_WORKER_RUNTIME is unset, then verify that the minified package provides the required workers directory without restoring unnecessary workers. Done means those scenarios no longer fail while minified packages retain their intended contents.

Written by the indexing model from the issue text.