Add forward-ref alias regression test for trailing-comment RHS

Codex flagged a ripper-only path where Constant#is_alias_for_path stays
nil for +Foo = Bar # comment+: parse_constant_body's on_const branch
only fires create_module_alias when the const token is followed by
on_nl/EOF, so the trailing comment short-circuits the recording. Pre-PR
this was masked by Constant#find_alias_for's lookup-time regex on
+value+, which this PR removes.

Skip the actual fix -- the ripper parser is on its way out (loads with
a deprecation banner, opt-in via RDOC_USE_RIPPER_PARSER=1) and isn't
worth a backstop. Keep the test in the shared parser-mixin
(RDocParserPrismTestCases) so prism is still guarded against the same
shape, and omit it under the legacy ripper variant.

Author: claude

test/rdoc/parser/prism_ruby_test.rb

@@ -1715,6 +1715,24 @@ class Bar; end
     assert_equal 'Foo::Bar', a_const.is_alias_for.full_name
   end
 
+  def test_constant_alias_with_trailing_comment_resolves_after_complete
+    omit if accept_legacy_bug? # ripper parser is deprecated; gap not worth fixing
+    util_parser <<~RUBY
+      class Foo
+        Trailing = Bar # trailing comment
+      end
+      class Bar; end
+    RUBY
+    @store.complete(:public)
+    foo = @store.classes_hash['Foo']
+    trailing = foo.constants.find { |c| c.name == 'Trailing' }
+    refute_nil trailing
+    refute_nil trailing.is_alias_for,
+      'a constant alias whose RHS is followed by a trailing comment ' \
+      'should still resolve to its target after Store#complete'
+    assert_equal 'Bar', trailing.is_alias_for.full_name
+  end
+
   def test_repeated_constant_alias
     util_parser <<~RUBY
       # Parsed first