Builtin support for nested comments or a canonical way to handle them

Currently, I use an approach [here](https://github.com/input-output-hk/plutus/blob/master/language-plutus-core/src/Language/PlutusCore/Lexer.x#L152), which is as far as I can tell the correct way to implement nested comments.

I'd also like to keep annotations which are kept in nested comments, which I imagine is possible but isn't straightforward to me. Ether a canonical example or builtin support would be wonderful.

Thanks!