Run Rails console test against IRB with Reline instead of Readline

1. By removing the `--singleline` flag, IRB will use Reline by default.
2. By assigning `TERM=dumb`, Reline will skip east-asian width detection,
   which was what caused the test to hang.

I need to stress that the east-asian width detection is not a bug but an
improvement in Reline to help rendering east-asian characters correctly.
Readline actually can't do this well. Please see @tompng's great explanation
in ruby/irb#582 (comment)

However, this detection should not happen when the terminal is running in
PTY (usually used in test environment). The problem is that in Ruby we
don't have a way to detect if the terminal is running in TTY or PTY.

But by passing `TERM=dumb`, Reline will assume that the terminal is not
capable of several advanced features, including this east-asian width
detection.

railties/test/application/console_test.rb

@@ -125,6 +125,7 @@ def write_prompt(command, expected_output = nil)
 
   def spawn_console(options, wait_for_prompt: true)
     pid = Process.spawn(
+      { "TERM" => "dumb" },
       "#{app_path}/bin/rails console #{options}",
       in: @replica, out: @replica, err: @replica
     )
@@ -137,7 +138,7 @@ def spawn_console(options, wait_for_prompt: true)
   end
 
   def test_sandbox
-    options = "--sandbox -- --singleline --nocolorize"
+    options = "--sandbox -- --nocolorize"
     spawn_console(options)
 
     write_prompt "Post.count", "=> 0"
@@ -165,7 +166,7 @@ def test_sandbox_when_sandbox_is_disabled
   end
 
   def test_environment_option_and_irb_option
-    options = "-e test -- --verbose --singleline --nocolorize"
+    options = "-e test -- --verbose --nocolorize"
     spawn_console(options)
 
     write_prompt "a = 1", "a = 1"

railties/test/engine/commands_test.rb

@@ -35,8 +35,8 @@ def test_runner_command_work_inside_engine
   if available_pty?
     def test_console_command_work_inside_engine
       primary, replica = PTY.open
-      cmd = "console --singleline"
-      spawn_command(cmd, replica)
+      cmd = "console"
+      spawn_command(cmd, replica, env: { "TERM" => "dumb" })
       assert_output(">", primary)
     ensure
       primary.puts "quit"
@@ -64,9 +64,9 @@ def plugin_path
       "#{@destination_root}/bukkits"
     end
 
-    def spawn_command(command, fd)
+    def spawn_command(command, fd, env: {})
       in_plugin_context(plugin_path) do
-        Process.spawn("bin/rails #{command}", in: fd, out: fd, err: fd)
+        Process.spawn(env, "bin/rails #{command}", in: fd, out: fd, err: fd)
       end
     end