Teach typo correction to properly handle mapping declarations to their

Teach typo correction to properly handle mapping declarations to their
underlying decls. Preserve the found declaration throughout, and only map to
the underlying declaration when we want to check whether it's the right kind.
This allows us to provide the right source location for the found declaration,
and prepares for the possibility of underlying decls with a different name
from the found decl.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@256575 91177308-0d34-0410-b5e6-96231b3b80d8