Formatter/ObjC: In dictionary literals, break after ':', not before it.

Before:
  @{ NSFontAttributeNameeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
     : regularFont, };

Now:
  @{ NSFontAttributeNameeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :
     regularFont, };

':'s in dictionary literals (and the corresponding {}s) are now marked as
TT_ObjCDictLiteral too, which makes further improvements to dict literal
layout possible.

llvm-svn: 182716