We Should Make the Slice Compiler Better Tolerate 'Bad' Identifiers

[InsertCreativityHere]

I'm not suggesting that we loosen our rules, or downgrade errors to warnings, just that we should change the parser to be more graceful when it encounters a Slice definitions that uses a 'bad' identifier.

For example, trying to compile this:

module _hello
{
    interface Foo {...}
}

produces 2 errors: one for illegal leading underscore in identifier ..., but another for interfaces can only be defined within a module.
This 2nd error is totally bogus. The interface was defined in a module.

---

What's happening is that if we hit a 'bad' name, we don't even bother creating the Slice definition internally.
So, when we parse this, we never create a new instance of Module (since it had a bad name), and when the parser sees an interface,
it looks at it's stack of container contexts and sees it's not in a Module: triggering an error.

The Slice compiler should always construct a new instance of these types, even if it's using a reserved identifier.
The only thing that should change when you use a bad identifier is that we emit an error message. That's it. Nothing else.