Expand metaprogramming for Symbol, Slash and Dot.

This first started with moving type method inside
`ActionDispatch::Journey::Nodes::Symbol`.

`AD::Journey::Nodes::Symbol#type` was generated dynamically with an
`each` block. While this is OK for classes like `AD::Journey::Nodes::Slash`
or `AD::Journey::Nodes::Dot` which don't have further implementation, all
other classes containing more logic have this method defined in their class
body. This patch does the same in this case.

On code review process @kamipo suggested to fully expand over
metaprogramming for Slash and Dot classes, a topic on which I agree with him.

actionpack/lib/action_dispatch/journey/nodes/node.rb

@@ -65,12 +65,12 @@ def initialize(x = Object.new)
         def literal?; false; end
       end
 
-      %w{ Symbol Slash Dot }.each do |t|
-        class_eval <<-eoruby, __FILE__, __LINE__ + 1
-          class #{t} < Terminal;
-            def type; :#{t.upcase}; end
-          end
-        eoruby
+      class Slash < Terminal # :nodoc:
+        def type; :SLASH; end
+      end
+
+      class Dot < Terminal # :nodoc:
+        def type; :DOT; end
       end
 
       class Symbol < Terminal # :nodoc:
@@ -89,6 +89,7 @@ def default_regexp?
           regexp == DEFAULT_EXP
         end
 
+        def type; :SYMBOL; end
         def symbol?; true; end
       end