[FEATURE] sap.m.ComboBox: keyboard handling support for DOWN/UP

DOWN/UP moves and changes the selection between items

DOWN

- change the selection to the next item from the picker and update the input field accordingly
- if the last item is already selected, do nothing

UP

- change the selection to the previous item from the picker and update the input field accordingly
- if the first matching item is already highlighted, do nothing

Change-Id: I1a3079e8f060a528e487cfb2f0d981067a222273
Merge "[FEATURE] sap.m.ComboBox: keyboard handling support for DOWN/UP"