Keyboard focus improvements for font features/axes

Adding an item is generally done by clicking the "add new" button and selecting an item from the flyout. However, when you do this from the keyboard, it feels a little weird. Your focus stays on the add new button.

Ideally, it would move to the newly added item.

This is particularly bad if the user added the last feature/axes. Since that disables the add new button, the button can't be focused, so it gets yeeted to the tab row.