Create easy-to-use `withProgress` stub helper, or remove all `withProgress` stubbing entirely

Most of the time, we're just trying to stub it to test whatever the inner function is that `withProgress` waits on, but handling that in Mocha tests is pretty gross and we have [a few different implementations](https://github.com/search?q=repo%3Aconfluentinc%2Fvscode%20withProgress%20path%3A*.test.ts&type=code) of it.

If we can't come up with an easy-to-use stub helper (like [the ones we have now](https://github.com/confluentinc/vscode/tree/main/tests/stubs)), we should do some refactoring so any `withProgress` calls are light wrappers around the actual-functions being tested. (One example of this is our [Kafka cluster quickpick](https://github.com/confluentinc/vscode/blob/fdd12d21a1391b821d571726ac03a6a74da62afe/src/quickpicks/kafkaClusters.ts#L21-L31).)