Allow access to the Ace editor instance

Please add the `aceEditor` property to the documentation and the `@types` so we can make small adjustments like controlling the `minLines` and `maxLines` settings?

Technically there is nothing preventing access. The property doesn't exist in the TypeScript declarations but that is easy to work around. But this change would just make things official and then it is unlikely that the property will become private or be renamed in the future.