Support recursive named tuples (#13371)
This is a continuation of #13297
The main change here is that although named tuples are still stored in symbol tables as `TypeInfo`s, when type analyzer sees them, it creates a `TypeAliasType` targeting what it would return before (a `TupleType` with a fallback to an instance of that `TypeInfo`). Although it is a significant change, IMO this is the simplest but still clean way to support recursive named tuples.
Also it is very simple to extend to TypedDicts, but I wanted to make the latter in a separate PR, to minimize the scope of changes.
It would be great if someone can take a look at this PR soon.
The most code changes are to make named tuples semantic analysis idempotent, previously they were analyzed "for real" only once, when all types were ready. It is not possible anymore if we want them to be recursive. So I pass in `existing_info` everywhere, and update it instead of creating a new one every time.
