Formatter: Move ObjC literal tests to its own test case.

Slightly expand the boxed expressions test with a few more snippets from
http://clang.llvm.org/docs/ObjectiveCLiterals.html



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174559 91177308-0d34-0410-b5e6-96231b3b80d8