Currently, Ruby's error printer escapes an error message.

```
$ ruby -e 'raise "foo\\bar"'
-e:1:in `<main>': foo\\bar (RuntimeError)
```

This change stops the behavior.

```
$ ruby -e 'raise "foo\\bar"'
-e:1:in `<main>': foo\bar (RuntimeError)
```

As a migration path, the behavior is kept when the message includes any
control character, with a warning is also printed.

```
$ ruby -e 'raise "\0"'
-e: warning: this error message is currently escaped because it includes control characters, but this will not be escaped in Ruby 3.3
-e:1:in `<main>': \0 (RuntimeError)
```

[Feature #18367]