Reimplement much of the way that we track nested classes in the

Reimplement much of the way that we track nested classes in the
parser. Rather than placing all of the delayed member function
declarations and inline definitions into a single bucket corresponding
to the top-level class, we instead mirror the nesting structure of the
nested classes and place the delayed member functions into their
appropriate place. Then, when we actually parse the delayed member
function declarations, set up the scope stack the same way as it was
when we originally saw the declaration, so that we can find, e.g.,
template parameters that are in scope.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@72502 91177308-0d34-0410-b5e6-96231b3b80d8