Bug 884703 - Remove inline styles on visual keys if present

Fix for [#884703](https://bugzilla.mozilla.org/show_bug.cgi?id=884703). When rotating we only apply `resizeUI` and don't re-render the whole UI. Therefore the style.width property on a visual key is still set and we get the value derived from that back in `visualKey.offsetWidth`. This patch removes the width before resizing the keys. The reason I don't do it inline is because it triggers a reflow for every key we apply this to, so rather do that at the beginning.

Tests for this change are in #10532.