[clang] Fix a bug with qualified name lookup into current instantiation (#73018)

Due to d0d2ee0e clang doesn't perform
qualified name lookup into the current instantiation when it has
dependent bases, because of that `getTypeName` call always returns null
for unknown specialization case. When there is a `typename` keyword,
`DependentNameType` is constructed instead of simply returning null.
This change attempts to do the same in case of `typename` absence.

Fixes https://github.com/llvm/llvm-project/issues/13826