Unit tests for LESS/SCSS

Also fixes for #8894 and #8895.
The main reason of combining the two cases is not for saving some lines of code. It is for handling both cases the right way since we want to skip all in both cases. We use `while (token !== ";")` to take care of the case where we don't have a `{ }` block, but using `_skipToClosingBracket("{");` to take care of the `{ }` block. And if there is any at-rule that we want to handle in the future, it should be done before `else` case here.