[Sema] Fix handling of enumerators used as default arguments of lambda

expressions in a function or class template.

This patch makes the following changes:

- Create a DependentScopeDeclRefExpr for the default argument instead of
  a CXXDependentScopeMemberExpr.
- Pass CombineWithOuterScope=true so that the outer scope in which the
  enum is declared is searched for the instantiation of the enum. 

This is the first part of https://reviews.llvm.org/D23096. Fixes PR28795

rdar://problem/27535319

llvm-svn: 289914