Formatter: Add support for @interface.

Previously:
@interface Foo + (id)init; @end

Now:
@interface Foo
+ (id)init;
@end

Some tweaking remains, but this is a good first step.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171995 91177308-0d34-0410-b5e6-96231b3b80d8
Fix test after r171995.

I wasn't aware libFormat is used elsewhere already. Let me know if rebasing
is not the right thing to do here.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171996 91177308-0d34-0410-b5e6-96231b3b80d8