Improve recovery when we see a dependent template name that is missing

the required "template" keyword, using the same heuristics we do for
dependent template names in member access expressions, e.g.,

test/SemaTemplate/dependent-template-recover.cpp:11:8: error: use 'template'
      keyword to treat 'getAs' as a dependent template name
    T::getAs<U>();
       ^
       template 

Fixes PR5404.

llvm-svn: 104409