refactor: simplify Input Group border-radius selector

refactor: simplify Input Group border-radius selector

We should assume as little as possible to HTML structure inside our components. People should be able to freely use the classes of components/elements we provide without limited by self-references and dependencies.

This commit simplify the selector used to apply border-radius on Input Group childreens to make all childreens affected, with a single exception for `.input-group-button` where sub-childreens are affected too.