When the left-hand side of an equality comparison is known to be a
String, and the equality condition resolves to true, then the right-hand
side can be smart-cast to a String as well. This was working for String
expressions on the left-hand side but not for String constants.
^KT-57513 Fixed
In order to make resolution still work for members not available from
`Nothing`, we track the type without `Nothing?` and use that for
resolution instead.
Brian Norman