String.prototype.replace does not work with replacement patterns

```console
> 'abc'.replaceAll(/(b)/g,'[$1]')
SmallString("a[$1]c")
> 'abc'.replaceAll(/(b)/g,'[$$]')
SmallString("a[$$]c")
```

Should be:
```console
> 'abc'.replaceAll(/(b)/g,'[$1]')
'a[b]c'
> 'abc'.replaceAll(/(b)/g,'[$$]')
'a[$]c'
```