Respect the project's development dependencies when running console tests

When investigating the issue related to ruby/irb#919,
I realized that console tests aren't executed with the IRB version specified
in the project's Gemfile. This is because the rdbg command passed to PTY process
doesn't use Bundler.

This commit changes the PTY's rdbg command to use Bundler if the test is
executed with it. This will make it significantly easier to
debug issues related to IRB or Reline changes.

Author: st0012

test/support/console_test_case.rb

@@ -120,7 +120,13 @@ def debug_code(program, remote: true, verbose: false, &test_steps)
     end
 
     def run_test_scenario cmd, test_info, verbose: false
-      PTY.spawn({ "HOME" => pty_home_dir }, cmd) do |read, write, pid|
+      env = { "HOME" => pty_home_dir }
+
+      if ENV.key?('BUNDLE_GEMFILE')
+        env["RUBYOPT"] = '-rbundler/setup'
+      end
+
+      PTY.spawn(env, cmd) do |read, write, pid|
         test_info.backlog = []
         test_info.last_backlog = []
         begin