fix: adjust Keyboard.findFocusable() - sort by tabindex
fix: adjust Keyboard.findFocusable() - sort by tabindex

This ensures first and last focusable are correct in situations where
specific tab ordering is in play

Example: https://codepen.io/d4mation/pen/KKMdPgW vs
https://codepen.io/d4mation/pen/jOrbNyB

DaSchTour/foundation-sites,DaSchTour/foundation-sites