Please make the HighlightQuery class public

We're using the highlighter directly in our code, and the introduction of the package-scoped HighlightQuery in 4aa59aff0058b05e822592431eda4a469a6b9eef has made this impossible without building our own little fork.
I do see the reason why we need to make the `HighlightQuery` public, but I'm not sure about the constructor. The object gets created by the HighlightPhase and ideally the highlighters would just rely in the instance created there.