[analyzer] Improve localizability checks for iOS / OS X.

[analyzer] Improve localizability checks for iOS / OS X.

Various improvements to the localization checker:
* Adjusted copy to be consistent with diagnostic text in other Apple
  API checkers.
* Added in ~150 UIKit / AppKit methods that require localized strings in
  UnlocalizedStringsChecker.
* UnlocalizedStringChecker now checks for UI methods up the class hierarchy and
  UI methods that conform for a certain Objective-C protocol.
* Added in alpha version of PluralMisuseChecker and some regression tests. False
  positives are still not ideal.

A patch by Kulpreet Chilana!

Differential Revision: http://reviews.llvm.org/D12417

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@248350 91177308-0d34-0410-b5e6-96231b3b80d8