8332901: Select{Current,New}ItemTest.java for Choice don't open popup on macOS
Move SelectCurrentItemTest.java to java/awt/Choice/SelectItem/.
Move SelectNewItemTest.java to java/awt/Choice/SelectItem/.
Use latches to control test flow instead of delays.
Encapsulate the common logic in SelectCurrentItemTest.
Provide overridable checkXXX() methods to modify conditions.
Provide an overridable method which defines where to click
in the choice popup to select an item.
Reviewed-by: honkar, prr, dnguyen