Remove literal? check to fix issue with prefixed optionals

In commit d993cb3 `build_path` was changed from using `grep` to
`find_all` to save array allocations.

This change was a little too aggressive in that when the dash comes
before the symbol like `/omg-:song` the symbol is skipped.

Removing the check for `n.right.left.literal?` fixes this issue, but
does add back some allocations. The number of allocations are still well
less than before.

I've added a regression test to test this behavior for the future.

Fixes #23069.

Array allocations as of d993cb3:

```
{:T_SYMBOL=>11}
{:T_REGEXP=>17}
{:T_STRUCT=>6500}
{:T_MATCH=>12004}
{:T_OBJECT=>91009}
{:T_DATA=>100088}
{:T_HASH=>114013}
{:T_STRING=>159637}
{:T_ARRAY=>321056}
{:T_IMEMO=>351133}
```

Array allocations after this change:

```
{:T_SYMBOL=>11}
{:T_REGEXP=>1017}
{:T_STRUCT=>6500}
{:T_MATCH=>12004}
{:T_DATA=>84092}
{:T_OBJECT=>87009}
{:T_HASH=>110015}
{:T_STRING=>166152}
{:T_ARRAY=>322056}
{:T_NODE=>343558}
```

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -187,7 +187,7 @@ def build_path(ast, requirements, anchor)
           # Get all the symbol nodes followed by literals that are not the
           # dummy node.
           symbols = ast.find_all { |n|
-            n.cat? && n.left.symbol? && n.right.cat? && n.right.left.literal?
+            n.cat? && n.left.symbol? && n.right.cat?
           }.map(&:left)
 
           # Get all the symbol nodes preceded by literals.

actionpack/test/controller/routing_test.rb

@@ -94,6 +94,18 @@ def test_symbols_with_dashes
     assert_equal({"artist"=>"journey", "song"=>"faithfully"}, hash)
   end
 
+  def test_symbols_with_dashes_reversed
+    rs.draw do
+      get ':artist(/omg-:song)', :to => lambda { |env|
+        resp = ActiveSupport::JSON.encode ActionDispatch::Request.new(env).path_parameters
+        [200, {}, [resp]]
+      }
+    end
+
+    hash = ActiveSupport::JSON.decode get(URI('http://example.org/journey/omg-faithfully'))
+    assert_equal({"artist"=>"journey", "song"=>"faithfully"}, hash)
+  end
+
   def test_id_with_dash
     rs.draw do
       get '/journey/:id', :to => lambda { |env|