Refactoring request: "Promote variable to parent scope/demote variable to child scope"

Essentially you have something like:

```csharp
if (someCondition)
{
var foo = bar();
}
```

and now you need to use `foo` outside of the conditional block, so you rewrite the code as:

```csharp
TypeOfFoo foo;

if (someCondition)
{
foo = bar();
}
```

Note that the RHS of the expression remains inside the conditional block; only the declaration moves. Doing this requires two steps: (1) moving the declaration (2) updating the declaration's type, and a refactoring that could do it in a single step would be most helpful. A complementary refactoring to go the other way (creating an anonymous scope to achieve this) would also probably be useful.