UX: Use button instead of anchor in filtered replies bar (PR #13439)

Fixes a subtle issue on laptops with touchscreens where hovering over the button would look bad:


The issue is that in our stylesheet’s we have a general hover style for anchors. That style gets overriden for button-like anchors (a.btn elements) but only for non-touch devices.

This is a bit tricky to fix generally, so this commit sidesteps the problem and uses a button element instead of an anchor in this specific scenario.