Refactor IndentState into two classes.

As we keep adding more stuff to it, this structure is easier to
maintain. At one point we might think about making it an actual
class with specific accessors, etc.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172188 91177308-0d34-0410-b5e6-96231b3b80d8