[analyzer] Add checkers for OS X / iOS localizability issues

Add checkers that detect code-level localizability issues for OS X / iOS:
 - A path sensitive checker that warns about uses of non-localized
 NSStrings passed to UI methods expecting localized strings.
 - A syntax checker that warns against not including a comment in
 NSLocalizedString macros.

A patch by Kulpreet Chilana!

llvm-svn: 244389