Fix expando object circularity in index inference

Fix circularity when assigning to expando object properties (6a6cb09)

The checker now excludes expando object literals from isObjectTypeWithInferableIndex, preventing them from being treated like plain object literals during index inference. That breaks the circular relationship seen when assigning properties like obj.foo and obj.buzz = Object.values(obj), and the new regression test locks in the corrected behavior.

Other misc changes

• Added regression baseline coverage for expandoNoInferredIndex symbols and types.