[ruby/irb] Filter out top-level methods when using `ls

<Class/Module>`
(ruby/irb#562)

Instead of always printing methods inherited from Class or Module, IRB by
default should filter them out unless `<Class/Module>` is specified to be
either of those.

lib/irb/cmd/ls.rb

@@ -39,8 +39,12 @@ def execute(*arg, grep: nil)
       def dump_methods(o, klass, obj)
         singleton_class = begin obj.singleton_class; rescue TypeError; nil end
         dumped_mods = Array.new
+        ancestors = klass.ancestors
+        ancestors = ancestors.reject { |c| c >= Object } if klass < Object
+        singleton_ancestors = (singleton_class&.ancestors || []).reject { |c| c >= Class }
+
         # singleton_class' ancestors should be at the front
-        maps = class_method_map(singleton_class&.ancestors || [], dumped_mods) + class_method_map(klass.ancestors, dumped_mods)
+        maps = class_method_map(singleton_ancestors, dumped_mods) + class_method_map(ancestors, dumped_mods)
         maps.each do |mod, methods|
           name = mod == singleton_class ? "#{klass}.methods" : "#{mod}#methods"
           o.dump(name, methods)
@@ -49,7 +53,6 @@ def dump_methods(o, klass, obj)
 
       def class_method_map(classes, dumped_mods)
         dumped_methods = Array.new
-        classes = classes.reject { |mod| mod >= Object }
         classes.map do |mod|
           next if dumped_mods.include? mod
 

test/irb/test_cmd.rb

@@ -697,6 +697,8 @@ def test_ls_class
       assert_empty err
       assert_match(/C2.methods:\s+m3\s+m5\n/, out)
       assert_match(/C2#methods:\s+m3\s+m4\n.*M1#methods:\s+m2\n.*C1#methods:\s+m1\n/, out)
+      assert_not_match(/Module#methods/, out)
+      assert_not_match(/Class#methods/, out)
     end
 
     def test_ls_module
@@ -716,8 +718,9 @@ def test_ls_module
       )
 
       assert_empty err
-      assert_match(/M2\.methods:\s+m4\nModule#methods:/, out)
+      assert_match(/M2\.methods:\s+m4\n/, out)
       assert_match(/M2#methods:\s+m1\s+m3\n.*M1#methods:\s+m2\n/, out)
+      assert_not_match(/Module#methods/, out)
     end
 
     def test_ls_instance