## Summary
We were over-conflating the conditions for deferred name resolution.
`from __future__ import annotations` defers annotations, but not class
bases. In stub files, class bases are also deferred. Modeling this
correctly also reduces likelihood of cycles in Python files using `from
__future__ import annotations` (since deferred resolution is inherently
cycle-prone). The same cycles are still possible in `.pyi` files, but
much less likely, since typically there isn't anything in a `pyi` file
that would cause an early return from a scope, or otherwise cause
visibility constraints to persist to end of scope. Usually there is only
code at module global scope and class scope, which can't have `return`
statements, and `raise` or `assert` statements in a stub file would be
very strange. (Technically according to the spec we'd be within our
rights to just forbid a whole bunch of syntax outright in a stub file,
but I kinda like minimizing unnecessary differences between the handling
of Python files and stub files.)
## Test Plan
Added mdtests.
1918c61623