[red-knot] Store the value type for name expressions in store context.

[MichaReiser]

Given:

class Name:
    ...

class Foo:
    name: Name

Red Knot stores Type::Never for the ExprName node declaring the attribute name. In pseudo code:

class Name:
    ...

class Foo:
    reveal_type(name): Name

Storing Type::Never has the downside that goto type definition and other LSP operations don't work as expected (unless we handle these expressions differently).

We should consider storing the new value type for the ExprName node instead.