Fix name resolver for class/module-alias

[ksss]

Fix https://github.com/ruby/rbs/issues/2293

Before

module M
  module N
  end

  # 2. Found the `::M::N2` and search the the `N`(`entry.decl.old_name`).
  # 3. The `::N` is nothing.
  module N2 = N 
end

class C
  # 1. Validate command search the `::M::N2`
  # 4. Report "The `M::N2` is not found".
  include M::N2
end

After

module M
  module N
  end

  # 2. Found `::M::N2` and search the `N`.
  # 3. `::N` is nothing.
  # 4. Search  the `::M::N`. (from `entry.outer`)
  # 5. Found the `::M::N`.
  module N2 = N 
end

class C
  # 1. Validate command search the `::M::N2`
  # 6. `M::N2` resolved by `::M::N`.
  include M::N2
end