`@layer` names are unescaped in output

[romainmenke]

playground

@layer one.two\20 three\#four\.five {
  one.two\20 three\#four\.five {
    background: \75 Rl(test.png);
  }
}

becomes :

@layer one.two three#four.five {
  one.two\ three\#four\.five {
    background: url("http://example.com/test.png");
  }
}

The selector escaping is handled correctly but the @layer name is not.

[devongovett]

Good catch. Looks like this should use serialize_identifier:

lightningcss/src/rules/layer.rs

Line 75 in 6fb7729

dest.write_str(name)?;