Add support for single quotes

[Yash-Singh1]

Strings currently can't be wrapped in single quotes, they have to be wrapped in double-quotes:

type function TrimLeft = (T) => ^{
    if (T extends `${infer space}${infer rest}`) {
        return ^{
            if (space extends ' ' /* error */) {
                return TrimLeft<rest>
            } else {
                return rest
            }
        }
    } else {
        return never
    }
}

[mistlog]

Yes, we only support double-quotes for consistent code style.

For example, in javascript, we can use both '' and "", then one day we will find that we need code formatter such as prettier to enforce one way to use quote, such as --single-quote option.

I guess that if we support only one way to do things like this, we don't need formatter for this purpose.