When we look up the types of class bases or keywords (`metaclass`), we
currently do this little dance: if there are type params, then look up
the type using `SemanticModel` in the type-params scope, if not, look up
the type directly in the definition's own scope, with support for
deferred types.
With inference of function parameter types, I'm now adding another case
of this same dance, so I'm motivated to make it a bit more ergonomic.
Add support to `definition_expression_ty` to handle any sub-expression
of a definition, whether it is in the definition's own scope or in a
type-params sub-scope.
Related to both #13693 and #14161.
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