Investigate and Improve Auto-imports

[sodic]

The restructuring (#1688) we've done for Wasp 0.12.0 introduced Wasp's SDK inside node_modules. Imported Wasp functionalities have finally become a normal NPM package.

This opens up an opportunity to greatly improve our DX.
However, our IDE support is a little flaky.

Import autosuggestions should suggest everything a user might want to import (regardless of whether there's already an existing import from that path) and nothing else.

In theory, for each symbol, we should check:

1. Does the IDE suggest the correct autoimport work (when this is the first symbol imported from that path)?
2. If not, does the IDE suggest an correct autoimport (when there already is an import from that path)?
3. Is the correct import suggestion the only import suggestion? We don't want to confuse users and accidentally expose our internals.

In reality, we won't have to do this for each of our public symbols. If we figure out what's going on and how we can best assist the IDE in figuring out what it should suggest, we'll be pretty sure it always works.