Combobox Escape key should revert the input value, not clear it

[0ddfell0w]

The combobox pattern, as written, suggests that Escape should clear the input. This makes perfect sense if the combobox input is initially empty, but when there was some value present upon the combobox being expanded, it may make more sense to revert to that initial value. In the case of a combobox that was empty before being expanded, it will indeed clear the button

Thoughts?

Related: #1066