Hide debugger hint after the input is submitted (#789)

If `output_modifier_proc`'s `complete` arg is true, it means the input is
submitted. In that case, debugger hint doesn't provide value to users
and adds noise to the output. So we hide it in such case.

lib/irb/debug.rb

@@ -64,7 +64,7 @@ def DEBUGGER__.capture_frames(*args)
             unless output.strip.empty?
               cmd = output.split(/\s/, 2).first
 
-              if DEBUGGER__.commands.key?(cmd)
+              if !complete && DEBUGGER__.commands.key?(cmd)
                 output = output.sub(/\n$/, " # debug command\n")
               end
             end

test/irb/yamatanooroti/test_rendering.rb

@@ -389,11 +389,15 @@ def test_debug_integration_hints_debugger_commands
     script.close
     start_terminal(40, 80, %W{ruby -I#{@pwd}/lib #{script.to_path}}, startup_message: 'start IRB')
     write("debug\n")
-    write("n")
+    write("pp 1\n")
+    write("pp 1")
     close
 
     screen = result.join("\n").sub(/\n*\z/, "\n")
-    assert_include(screen, "irb:rdbg(main):002> n # debug command")
+    # submitted input shouldn't contain hint
+    assert_include(screen, "irb:rdbg(main):002> pp 1\n")
+    # unsubmitted input should contain hint
+    assert_include(screen, "irb:rdbg(main):003> pp 1 # debug command\n")
   ensure
     File.unlink(script) if script
   end